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FIO(1) - Linux manual page online | User commands

Flexible I/O tester.

August 2017
fio(1) General Commands Manual fio(1)


fio - flexible I/O tester


fio [options] [jobfile]...


fio is a tool that will spawn a number of threads or processes doing a particular type of I/O action as specified by the user. The typical use of fio is to write a job file match‐ ing the I/O load one wants to simulate.


--debug=type Enable verbose tracing type of various fio actions. May be `all' for all types or individual types separated by a comma (e.g. `--debug=file,mem' will enable file and memory debugging). `help' will list all available tracing options. --parse-only Parse options only, don't start any I/O. --output=filename Write output to filename. --output-format=format Set the reporting format to `normal', `terse', `json', or `json+'. Multiple formats can be selected, separate by a comma. `terse' is a CSV based format. `json+' is like `json', except it adds a full dump of the latency buckets. --bandwidth-log Generate aggregate bandwidth logs. --minimal Print statistics in a terse, semicolon-delimited format. --append-terse Print statistics in selected mode AND terse, semicolon-delimited format. Depre‐ cated, use --output-format instead to select multiple formats. --terse-version=version Set terse version output format (default `3', or `2', `4', `5'). --version Print version information and exit. --help Print a summary of the command line options and exit. --cpuclock-test Perform test and validation of internal CPU clock. --crctest=[test] Test the speed of the built-in checksumming functions. If no argument is given, all of them are tested. Alternatively, a comma separated list can be passed, in which case the given ones are tested. --cmdhelp=command Print help information for command. May be `all' for all commands. --enghelp=[ioengine[,command]] List all commands defined by ioengine, or print help for command defined by ioengine. If no ioengine is given, list all available ioengines. --showcmd=jobfile Convert jobfile to a set of command-line options. --readonly Turn on safety read-only checks, preventing writes. The --readonly option is an extra safety guard to prevent users from accidentally starting a write workload when that is not desired. Fio will only write if `rw=write/randwrite/rw/randrw' is given. This extra safety net can be used as an extra precaution as --readonly will also enable a write check in the I/O engine core to prevent writes due to unknown user space bug(s). --eta=when Specifies when real-time ETA estimate should be printed. when may be `always', `never' or `auto'. --eta-newline=time Force a new line for every time period passed. When the unit is omitted, the value is interpreted in seconds. --status-interval=time Force a full status dump of cumulative (from job start) values at time intervals. This option does *not* provide per-period measurements. So values such as bandwidth are running averages. When the time unit is omitted, time is interpreted in sec‐ onds. --section=name Only run specified section name in job file. Multiple sections can be specified. The --section option allows one to combine related jobs into one file. E.g. one job file could define light, moderate, and heavy sections. Tell fio to run only the "heavy" section by giving `--section=heavy' command line option. One can also spec‐ ify the "write" operations in one section and "verify" operation in another sec‐ tion. The --section option only applies to job sections. The reserved *global* sec‐ tion is always parsed and used. --alloc-size=kb Set the internal smalloc pool size to kb in KiB. The --alloc-size switch allows one to use a larger pool size for smalloc. If running large jobs with randommap enabled, fio can run out of memory. Smalloc is an internal allocator for shared structures from a fixed size memory pool and can grow to 16 pools. The pool size defaults to 16MiB. NOTE: While running `.fio_smalloc.*' backing store files are visible in `/tmp'. --warnings-fatal All fio parser warnings are fatal, causing fio to exit with an error. --max-jobs=nr Set the maximum number of threads/processes to support to nr. --server=args Start a backend server, with args specifying what to listen to. See CLIENT/SERVER section. --daemonize=pidfile Background a fio server, writing the pid to the given pidfile file. --client=hostname Instead of running the jobs locally, send and run them on the given hostname or set of hostnames. See CLIENT/SERVER section. --remote-config=file Tell fio server to load this local file. --idle-prof=option Report CPU idleness. option is one of the following: calibrate Run unit work calibration only and exit. system Show aggregate system idleness and unit work. percpu As system but also show per CPU idleness. --inflate-log=log Inflate and output compressed log. --trigger-file=file Execute trigger command when file exists. --trigger-timeout=time Execute trigger at this time. --trigger=command Set this command as local trigger. --trigger-remote=command Set this command as remote trigger. --aux-path=path Use this path for fio state generated files.


Any parameters following the options will be assumed to be job files, unless they match a job file parameter. Multiple job files can be listed and each job file will be regarded as a separate group. Fio will stonewall execution between each group. Fio accepts one or more job files describing what it is supposed to do. The job file for‐ mat is the classic ini file, where the names enclosed in [] brackets define the job name. You are free to use any ASCII name you want, except *global* which has special meaning. Following the job name is a sequence of zero or more parameters, one per line, that define the behavior of the job. If the first character in a line is a ';' or a '#', the entire line is discarded as a comment. A *global* section sets defaults for the jobs described in that file. A job may override a *global* section parameter, and a job file may even have several *global* sections if so desired. A job is only affected by a *global* section residing above it. The --cmdhelp option also lists all options. If used with an command argument, --cmdhelp will detail the given command. See the `examples/' directory for inspiration on how to write job files. Note the copy‐ right and license requirements currently apply to `examples/' files.


Some parameters take an option of a given type, such as an integer or a string. Anywhere a numeric value is required, an arithmetic expression may be used, provided it is surrounded by parentheses. Supported operators are: addition (+) subtraction (-) multiplication (*) division (/) modulus (%) exponentiation (^) For time values in expressions, units are microseconds by default. This is different than for time values not in expressions (not enclosed in parentheses).


The following parameter types are used. str String. A sequence of alphanumeric characters. time Integer with possible time suffix. Without a unit value is interpreted as seconds unless otherwise specified. Accepts a suffix of 'd' for days, 'h' for hours, 'm' for minutes, 's' for seconds, 'ms' (or 'msec') for milliseconds and 'us' (or 'usec') for microseconds. For example, use 10m for 10 minutes. int Integer. A whole number value, which may contain an integer prefix and an integer suffix. [*integer prefix*] **number** [*integer suffix*] The optional *integer prefix* specifies the number's base. The default is decimal. *0x* specifies hexadecimal. The optional *integer suffix* specifies the number's units, and includes an optional unit prefix and an optional unit. For quantities of data, the default unit is bytes. For quantities of time, the default unit is seconds unless otherwise specified. With `kb_base=1000', fio follows international standards for unit prefixes. To specify power-of-10 decimal values defined in the International System of Units (SI): K means kilo (K) or 1000 M means mega (M) or 1000**2 G means giga (G) or 1000**3 T means tera (T) or 1000**4 P means peta (P) or 1000**5 To specify power-of-2 binary values defined in IEC 80000-13: Ki means kibi (Ki) or 1024 Mi means mebi (Mi) or 1024**2 Gi means gibi (Gi) or 1024**3 Ti means tebi (Ti) or 1024**4 Pi means pebi (Pi) or 1024**5 With `kb_base=1024' (the default), the unit prefixes are opposite from those speci‐ fied in the SI and IEC 80000-13 standards to provide compatibility with old scripts. For example, 4k means 4096. For quantities of data, an optional unit of 'B' may be included (e.g., 'kB' is the same as 'k'). The *integer suffix* is not case sensitive (e.g., m/mi mean mebi/mega, not milli). 'b' and 'B' both mean byte, not bit. Examples with `kb_base=1000': 4 KiB: 4096, 4096b, 4096B, 4k, 4kb, 4kB, 4K, 4KB 1 MiB: 1048576, 1m, 1024k 1 MB: 1000000, 1mi, 1000ki 1 TiB: 1073741824, 1t, 1024m, 1048576k 1 TB: 1000000000, 1ti, 1000mi, 1000000ki Examples with `kb_base=1024' (default): 4 KiB: 4096, 4096b, 4096B, 4k, 4kb, 4kB, 4K, 4KB 1 MiB: 1048576, 1m, 1024k 1 MB: 1000000, 1mi, 1000ki 1 TiB: 1073741824, 1t, 1024m, 1048576k 1 TB: 1000000000, 1ti, 1000mi, 1000000ki To specify times (units are not case sensitive): D means days H means hours M mean minutes s or sec means seconds (default) ms or msec means milliseconds us or usec means microseconds If the option accepts an upper and lower range, use a colon ':' or minus '-' to separate such values. See irange parameter type. If the lower value specified hap‐ pens to be larger than the upper value the two values are swapped. bool Boolean. Usually parsed as an integer, however only defined for true and false (1 and 0). irange Integer range with suffix. Allows value range to be given, such as 1024-4096. A colon may also be used as the separator, e.g. 1k:4k. If the option allows two sets of ranges, they can be specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see int parameter type. float_list A list of floating point numbers, separated by a ':' character.


With the above in mind, here follows the complete list of fio job parameters. Units kb_base=int Select the interpretation of unit prefixes in input parameters. 1000 Inputs comply with IEC 80000-13 and the International System of Units (SI). Use: - power-of-2 values with IEC prefixes (e.g., KiB) - power-of-10 values with SI prefixes (e.g., kB) 1024 Compatibility mode (default). To avoid breaking old scripts: - power-of-2 values with SI prefixes - power-of-10 values with IEC prefixes See bs for more details on input parameters. Outputs always use correct prefixes. Most outputs include both side-by-side, like: bw=2383.3kB/s (2327.4KiB/s) If only one value is reported, then kb_base selects the one to use: 1000 -- SI prefixes 1024 -- IEC prefixes unit_base=int Base unit for reporting. Allowed values are: 0 Use auto-detection (default). 8 Byte based. 1 Bit based. Job description name=str ASCII name of the job. This may be used to override the name printed by fio for this job. Otherwise the job name is used. On the command line this parameter has the special purpose of also signaling the start of a new job. description=str Text description of the job. Doesn't do anything except dump this text description when this job is run. It's not parsed. loops=int Run the specified number of iterations of this job. Used to repeat the same work‐ load a given number of times. Defaults to 1. numjobs=int Create the specified number of clones of this job. Each clone of job is spawned as an independent thread or process. May be used to setup a larger number of threads/processes doing the same thing. Each thread is reported separately; to see statistics for all clones as a whole, use group_reporting in conjunction with new_group. See --max-jobs. Default: 1. Time related parameters runtime=time Tell fio to terminate processing after the specified period of time. It can be quite hard to determine for how long a specified job will run, so this parameter is handy to cap the total runtime to a given time. When the unit is omitted, the value is intepreted in seconds. time_based If set, fio will run for the duration of the runtime specified even if the file(s) are completely read or written. It will simply loop over the same workload as many times as the runtime allows. startdelay=irange(int) Delay the start of job for the specified amount of time. Can be a single value or a range. When given as a range, each thread will choose a value randomly from within the range. Value is in seconds if a unit is omitted. ramp_time=time If set, fio will run the specified workload for this amount of time before logging any performance numbers. Useful for letting performance settle before logging results, thus minimizing the runtime required for stable results. Note that the ramp_time is considered lead in time for a job, thus it will increase the total runtime if a special timeout or runtime is specified. When the unit is omitted, the value is given in seconds. clocksource=str Use the given clocksource as the base of timing. The supported options are: gettimeofday gettimeofday(2) clock_gettime clock_gettime(2) cpu Internal CPU clock source cpu is the preferred clocksource if it is reliable, as it is very fast (and fio is heavy on time calls). Fio will automatically use this clocksource if it's supported and considered reliable on the system it is running on, unless another clocksource is specifically set. For x86/x86-64 CPUs, this means supporting TSC Invariant. gtod_reduce=bool Enable all of the gettimeofday(2) reducing options (disable_clat, disable_slat, disable_bw_measurement) plus reduce precision of the timeout somewhat to really shrink the gettimeofday(2) call count. With this option enabled, we only do about 0.4% of the gettimeofday(2) calls we would have done if all time keeping was enabled. gtod_cpu=int Sometimes it's cheaper to dedicate a single thread of execution to just getting the current time. Fio (and databases, for instance) are very intensive on gettimeof‐ day(2) calls. With this option, you can set one CPU aside for doing nothing but logging current time to a shared memory location. Then the other threads/processes that run I/O workloads need only copy that segment, instead of entering the kernel with a gettimeofday(2) call. The CPU set aside for doing these time calls will be excluded from other uses. Fio will manually clear it from the CPU mask of other jobs. Target file/device directory=str Prefix filenames with this directory. Used to place files in a different location than `./'. You can specify a number of directories by separating the names with a ':' character. These directories will be assigned equally distributed to job clones created by numjobs as long as they are using generated filenames. If specific file‐ name(s) are set fio will use the first listed directory, and thereby matching the filename semantic which generates a file each clone if not specified, but let all clones use the same if set. See the filename option for information on how to escape ':' and '´ characters within the directory path itself. filename=str Fio normally makes up a filename based on the job name, thread number, and file number (see filename_format). If you want to share files between threads in a job or several jobs with fixed file paths, specify a filename for each of them to over‐ ride the default. If the ioengine is file based, you can specify a number of files by separating the names with a ':' colon. So if you wanted a job to open `/dev/sda' and `/dev/sdb' as the two working files, you would use `file‐ name=/dev/sda:/dev/sdb'. This also means that whenever this option is specified, nrfiles is ignored. The size of regular files specified by this option will be size divided by number of files unless an explicit size is specified by filesize. Each colon and backslash in the wanted path must be escaped with a '´ character. For instance, if the path is `/dev/dsk/foo@3,0:c' then you would use `file‐ name=/dev/dsk/foo@3,0\:c' and if the path is `F:\\filename' then you would use `filename=F\:\\filename'. On Windows, disk devices are accessed as `\\\\.\\PhysicalDrive0' for the first device, `\\\\.\\PhysicalDrive1' for the second etc. Note: Windows and FreeBSD pre‐ vent write access to areas of the disk containing in-use data (e.g. filesystems). The filename `-' is a reserved name, meaning *stdin* or *stdout*. Which of the two depends on the read/write direction set. filename_format=str If sharing multiple files between jobs, it is usually necessary to have fio gener‐ ate the exact names that you want. By default, fio will name a file based on the default file format specification of `jobname.jobnumber.filenumber'. With this option, that can be customized. Fio will recognize and replace the following key‐ words in this string: $jobname The name of the worker thread or process. $jobnum The incremental number of the worker thread or process. $filenum The incremental number of the file for that worker thread or process. To have dependent jobs share a set of files, this option can be set to have fio generate filenames that are shared between the two. For instance, if `test‐ files.$filenum' is specified, file number 4 for any job will be named `test‐ files.4'. The default of `$jobname.$jobnum.$filenum' will be used if no other for‐ mat specifier is given. unique_filename=bool To avoid collisions between networked clients, fio defaults to prefixing any gener‐ ated filenames (with a directory specified) with the source of the client connect‐ ing. To disable this behavior, set this option to 0. opendir=str Recursively open any files below directory str. lockfile=str Fio defaults to not locking any files before it does I/O to them. If a file or file descriptor is shared, fio can serialize I/O to that file to make the end result consistent. This is usual for emulating real workloads that share files. The lock modes are: none No locking. The default. exclusive Only one thread or process may do I/O at a time, excluding all oth‐ ers. readwrite Read-write locking on the file. Many readers may access the file at the same time, but writes get exclusive access. nrfiles=int Number of files to use for this job. Defaults to 1. The size of files will be size divided by this unless explicit size is specified by filesize. Files are created for each thread separately, and each file will have a file number within its name by default, as explained in filename section. openfiles=int Number of files to keep open at the same time. Defaults to the same as nrfiles, can be set smaller to limit the number simultaneous opens. file_service_type=str Defines how fio decides which file from a job to service next. The following types are defined: random Choose a file at random. roundrobin Round robin over opened files. This is the default. sequential Finish one file before moving on to the next. Multiple files can still be open depending on openfiles. zipf Use a Zipf distribution to decide what file to access. pareto Use a Pareto distribution to decide what file to access. normal Use a Gaussian (normal) distribution to decide what file to access. gauss Alias for normal. For random, roundrobin, and sequential, a postfix can be appended to tell fio how many I/Os to issue before switching to a new file. For example, specifying `file_service_type=random:8' would cause fio to issue 8 I/Os before selecting a new file at random. For the non-uniform distributions, a floating point postfix can be given to influence how the distribution is skewed. See random_distribution for a description of how that would work. ioscheduler=str Attempt to switch the device hosting the file to the specified I/O scheduler before running. create_serialize=bool If true, serialize the file creation for the jobs. This may be handy to avoid interleaving of data files, which may greatly depend on the filesystem used and even the number of processors in the system. Default: true. create_fsync=bool fsync(2) the data file after creation. This is the default. create_on_open=bool If true, don't pre-create files but allow the job's open() to create a file when it's time to do I/O. Default: false -- pre-create all necessary files when the job starts. create_only=bool If true, fio will only run the setup phase of the job. If files need to be laid out or updated on disk, only that will be done -- the actual job contents are not exe‐ cuted. Default: false. allow_file_create=bool If true, fio is permitted to create files as part of its workload. If this option is false, then fio will error out if the files it needs to use don't already exist. Default: true. allow_mounted_write=bool If this isn't set, fio will abort jobs that are destructive (e.g. that write) to what appears to be a mounted device or partition. This should help catch creating inadvertently destructive tests, not realizing that the test will destroy data on the mounted file system. Note that some platforms don't allow writing against a mounted device regardless of this option. Default: false. pre_read=bool If this is given, files will be pre-read into memory before starting the given I/O operation. This will also clear the invalidate flag, since it is pointless to pre-read and then drop the cache. This will only work for I/O engines that are seek-able, since they allow you to read the same data multiple times. Thus it will not work on non-seekable I/O engines (e.g. network, splice). Default: false. unlink=bool Unlink the job files when done. Not the default, as repeated runs of that job would then waste time recreating the file set again and again. Default: false. unlink_each_loop=bool Unlink job files after each iteration or loop. Default: false. zonesize=int Divide a file into zones of the specified size. See zoneskip. zonerange=int Give size of an I/O zone. See zoneskip. zoneskip=int Skip the specified number of bytes when zonesize data has been read. The two zone options can be used to only do I/O on zones of a file. I/O type direct=bool If value is true, use non-buffered I/O. This is usually O_DIRECT. Note that OpenBSD and ZFS on Solaris don't support direct I/O. On Windows the synchronous ioengines don't support direct I/O. Default: false. atomic=bool If value is true, attempt to use atomic direct I/O. Atomic writes are guaranteed to be stable once acknowledged by the operating system. Only Linux supports O_ATOMIC right now. buffered=bool If value is true, use buffered I/O. This is the opposite of the direct option. Defaults to true. readwrite=str, rw=str Type of I/O pattern. Accepted values are: read Sequential reads. write Sequential writes. trim Sequential trims (Linux block devices only). randread Random reads. randwrite Random writes. randtrim Random trims (Linux block devices only). rw,readwrite Sequential mixed reads and writes. randrw Random mixed reads and writes. trimwrite Sequential trim+write sequences. Blocks will be trimmed first, then the same blocks will be written to. Fio defaults to read if the option is not specified. For the mixed I/O types, the default is to split them 50/50. For certain types of I/O the result may still be skewed a bit, since the speed may be different. It is possible to specify the number of I/Os to do before getting a new offset by appending `:<nr>' to the end of the string given. For a random read, it would look like `rw=randread:8' for passing in an offset modifier with a value of 8. If the suffix is used with a sequential I/O pattern, then the `<nr>' value specified will be added to the generated offset for each I/O turning sequential I/O into sequen‐ tial I/O with holes. For instance, using `rw=write:4k' will skip 4k for every write. Also see the rw_sequencer option. rw_sequencer=str If an offset modifier is given by appending a number to the `rw=str' line, then this option controls how that number modifies the I/O offset being generated. Accepted values are: sequential Generate sequential offset. identical Generate the same offset. sequential is only useful for random I/O, where fio would normally generate a new random offset for every I/O. If you append e.g. 8 to randread, you would get a new random offset for every 8 I/Os. The result would be a seek for only every 8 I/Os, instead of for every I/O. Use `rw=randread:8' to specify that. As sequential I/O is already sequential, setting sequential for that would not result in any differ‐ ences. identical behaves in a similar fashion, except it sends the same offset 8 number of times before generating a new offset. unified_rw_reporting=bool Fio normally reports statistics on a per data direction basis, meaning that reads, writes, and trims are accounted and reported separately. If this option is set fio sums the results and report them as "mixed" instead. randrepeat=bool Seed the random number generator used for random I/O patterns in a predictable way so the pattern is repeatable across runs. Default: true. allrandrepeat=bool Seed all random number generators in a predictable way so results are repeatable across runs. Default: false. randseed=int Seed the random number generators based on this seed value, to be able to control what sequence of output is being generated. If not set, the random sequence depends on the randrepeat setting. fallocate=str Whether pre-allocation is performed when laying down files. Accepted values are: none Do not pre-allocate space. native Use a platform's native pre-allocation call but fall back to none behavior if it fails/is not implemented. posix Pre-allocate via posix_fallocate(3). keep Pre-allocate via fallocate(2) with FALLOC_FL_KEEP_SIZE set. 0 Backward-compatible alias for none. 1 Backward-compatible alias for posix. May not be available on all supported platforms. keep is only available on Linux. If using ZFS on Solaris this cannot be set to posix because ZFS doesn't support pre-allocation. Default: native if any pre-allocation methods are available, none if not. fadvise_hint=str Use posix_fadvise(2) to advise the kernel what I/O patterns are likely to be issued. Accepted values are: 0 Backwards compatible hint for "no hint". 1 Backwards compatible hint for "advise with fio workload type". This uses FADV_RANDOM for a random workload, and FADV_SEQUENTIAL for a sequential workload. sequential Advise using FADV_SEQUENTIAL. random Advise using FADV_RANDOM. write_hint=str Use fcntl(2) to advise the kernel what life time to expect from a write. Only sup‐ ported on Linux, as of version 4.13. Accepted values are: none No particular life time associated with this file. short Data written to this file has a short life time. medium Data written to this file has a medium life time. long Data written to this file has a long life time. extreme Data written to this file has a very long life time. The values are all relative to each other, and no absolute meaning should be asso‐ ciated with them. offset=int Start I/O at the provided offset in the file, given as either a fixed size in bytes or a percentage. If a percentage is given, the next blockalign-ed offset will be used. Data before the given offset will not be touched. This effectively caps the file size at `real_size - offset'. Can be combined with size to constrain the start and end range of the I/O workload. A percentage can be specified by a number between 1 and 100 followed by '%', for example, `offset=20%' to specify 20%. offset_increment=int If this is provided, then the real offset becomes `offset + offset_increment * thread_number', where the thread number is a counter that starts at 0 and is incre‐ mented for each sub-job (i.e. when numjobs option is specified). This option is useful if there are several jobs which are intended to operate on a file in paral‐ lel disjoint segments, with even spacing between the starting points. number_ios=int Fio will normally perform I/Os until it has exhausted the size of the region set by size, or if it exhaust the allocated time (or hits an error condition). With this setting, the range/size can be set independently of the number of I/Os to perform. When fio reaches this number, it will exit normally and report status. Note that this does not extend the amount of I/O that will be done, it will only stop fio if this condition is met before other end-of-job criteria. fsync=int If writing to a file, issue an fsync(2) (or its equivalent) of the dirty data for every number of blocks given. For example, if you give 32 as a parameter, fio will sync the file after every 32 writes issued. If fio is using non-buffered I/O, we may not sync the file. The exception is the sg I/O engine, which synchronizes the disk cache anyway. Defaults to 0, which means fio does not periodically issue and wait for a sync to complete. Also see end_fsync and fsync_on_close. fdatasync=int Like fsync but uses fdatasync(2) to only sync data and not metadata blocks. In Win‐ dows, FreeBSD, and DragonFlyBSD there is no fdatasync(2) so this falls back to using fsync(2). Defaults to 0, which means fio does not periodically issue and wait for a data-only sync to complete. write_barrier=int Make every N-th write a barrier write. sync_file_range=str:int Use sync_file_range(2) for every int number of write operations. Fio will track range of writes that have happened since the last sync_file_range(2) call. str can currently be one or more of: wait_before SYNC_FILE_RANGE_WAIT_BEFORE write SYNC_FILE_RANGE_WRITE wait_after SYNC_FILE_RANGE_WRITE_AFTER So if you do `sync_file_range=wait_before,write:8', fio would use `SYNC_FILE_RANGE_WAIT_BEFORE | SYNC_FILE_RANGE_WRITE' for every 8 writes. Also see the sync_file_range(2) man page. This option is Linux specific. overwrite=bool If true, writes to a file will always overwrite existing data. If the file doesn't already exist, it will be created before the write phase begins. If the file exists and is large enough for the specified write phase, nothing will be done. Default: false. end_fsync=bool If true, fsync(2) file contents when a write stage has completed. Default: false. fsync_on_close=bool If true, fio will fsync(2) a dirty file on close. This differs from end_fsync in that it will happen on every file close, not just at the end of the job. Default: false. rwmixread=int Percentage of a mixed workload that should be reads. Default: 50. rwmixwrite=int Percentage of a mixed workload that should be writes. If both rwmixread and rwmixwrite is given and the values do not add up to 100%, the latter of the two will be used to override the first. This may interfere with a given rate setting, if fio is asked to limit reads or writes to a certain rate. If that is the case, then the distribution may be skewed. Default: 50. random_distribution=str:float[,str:float][,str:float] By default, fio will use a completely uniform random distribution when asked to perform random I/O. Sometimes it is useful to skew the distribution in specific ways, ensuring that some parts of the data is more hot than others. fio includes the following distribution models: random Uniform random distribution zipf Zipf distribution pareto Pareto distribution normal Normal (Gaussian) distribution zoned Zoned random distribution When using a zipf or pareto distribution, an input value is also needed to define the access pattern. For zipf, this is the `Zipf theta'. For pareto, it's the `Pareto power'. Fio includes a test program, fio-genzipf, that can be used visual‐ ize what the given input values will yield in terms of hit rates. If you wanted to use zipf with a `theta' of 1.2, you would use `random_distribution=zipf:1.2' as the option. If a non-uniform model is used, fio will disable use of the random map. For the normal distribution, a normal (Gaussian) deviation is supplied as a value between 0 and 100. For a zoned distribution, fio supports specifying percentages of I/O access that should fall within what range of the file or device. For example, given a criteria of: 60% of accesses should be to the first 10% 30% of accesses should be to the next 20% 8% of accesses should be to the next 30% 2% of accesses should be to the next 40% we can define that through zoning of the random accesses. For the above example, the user would do: random_distribution=zoned:60/10:30/20:8/30:2/40 similarly to how bssplit works for setting ranges and percentages of block sizes. Like bssplit, it's possible to specify separate zones for reads, writes, and trims. If just one set is given, it'll apply to all of them. percentage_random=int[,int][,int] For a random workload, set how big a percentage should be random. This defaults to 100%, in which case the workload is fully random. It can be set from anywhere from 0 to 100. Setting it to 0 would make the workload fully sequential. Any setting in between will result in a random mix of sequential and random I/O, at the given per‐ centages. Comma-separated values may be specified for reads, writes, and trims as described in blocksize. norandommap Normally fio will cover every block of the file when doing random I/O. If this option is given, fio will just get a new random offset without looking at past I/O history. This means that some blocks may not be read or written, and that some blocks may be read/written more than once. If this option is used with verify and multiple blocksizes (via bsrange), only intact blocks are verified, i.e., par‐ tially-overwritten blocks are ignored. softrandommap=bool See norandommap. If fio runs with the random block map enabled and it fails to allocate the map, if this option is set it will continue without a random block map. As coverage will not be as complete as with random maps, this option is dis‐ abled by default. random_generator=str Fio supports the following engines for generating I/O offsets for random I/O: tausworthe Strong 2^88 cycle random number generator. lfsr Linear feedback shift register generator. tausworthe64 Strong 64-bit 2^258 cycle random number generator. tausworthe is a strong random number generator, but it requires tracking on the side if we want to ensure that blocks are only read or written once. lfsr guaran‐ tees that we never generate the same offset twice, and it's also less computation‐ ally expensive. It's not a true random generator, however, though for I/O purposes it's typically good enough. lfsr only works with single block sizes, not with work‐ loads that use multiple block sizes. If used with such a workload, fio may read or write some blocks multiple times. The default value is tausworthe, unless the required space exceeds 2^32 blocks. If it does, then tausworthe64 is selected auto‐ matically. Block size blocksize=int[,int][,int], bs=int[,int][,int] The block size in bytes used for I/O units. Default: 4096. A single value applies to reads, writes, and trims. Comma-separated values may be specified for reads, writes, and trims. A value not terminated in a comma applies to subsequent types. Examples: bs=256k means 256k for reads, writes and trims. bs=8k,32k means 8k for reads, 32k for writes and trims. bs=8k,32k, means 8k for reads, 32k for writes, and default for trims. bs=,8k means default for reads, 8k for writes and trims. bs=,8k, means default for reads, 8k for writes, and default for trims. blocksize_range=irange[,irange][,irange], bsrange=irange[,irange][,irange] A range of block sizes in bytes for I/O units. The issued I/O unit will always be a multiple of the minimum size, unless blocksize_unaligned is set. Comma-separated ranges may be specified for reads, writes, and trims as described in blocksize. Example: bsrange=1k-4k,2k-8k bssplit=str[,str][,str] Sometimes you want even finer grained control of the block sizes issued, not just an even split between them. This option allows you to weight various block sizes, so that you are able to define a specific amount of block sizes issued. The format for this option is: bssplit=blocksize/percentage:blocksize/percentage for as many block sizes as needed. So if you want to define a workload that has 50% 64k blocks, 10% 4k blocks, and 40% 32k blocks, you would write: bssplit=4k/10:64k/50:32k/40 Ordering does not matter. If the percentage is left blank, fio will fill in the remaining values evenly. So a bssplit option like this one: bssplit=4k/50:1k/:32k/ would have 50% 4k ios, and 25% 1k and 32k ios. The percentages always add up to 100, if bssplit is given a range that adds up to more, it will error out. Comma-separated values may be specified for reads, writes, and trims as described in blocksize. If you want a workload that has 50% 2k reads and 50% 4k reads, while having 90% 4k writes and 10% 8k writes, you would specify: bssplit=2k/50:4k/50,4k/90,8k/10 blocksize_unaligned, bs_unaligned If set, fio will issue I/O units with any size within blocksize_range, not just multiples of the minimum size. This typically won't work with direct I/O, as that normally requires sector alignment. bs_is_seq_rand=bool If this option is set, fio will use the normal read,write blocksize settings as sequential,random blocksize settings instead. Any random read or write will use the WRITE blocksize settings, and any sequential read or write will use the READ block‐ size settings. blockalign=int[,int][,int], ba=int[,int][,int] Boundary to which fio will align random I/O units. Default: blocksize. Minimum alignment is typically 512b for using direct I/O, though it usually depends on the hardware block size. This option is mutually exclusive with using a random map for files, so it will turn off that option. Comma-separated values may be specified for reads, writes, and trims as described in blocksize. Buffers and memory zero_buffers Initialize buffers with all zeros. Default: fill buffers with random data. refill_buffers If this option is given, fio will refill the I/O buffers on every submit. The default is to only fill it at init time and reuse that data. Only makes sense if zero_buffers isn't specified, naturally. If data verification is enabled, refill_buffers is also automatically enabled. scramble_buffers=bool If refill_buffers is too costly and the target is using data deduplication, then setting this option will slightly modify the I/O buffer contents to defeat normal de-dupe attempts. This is not enough to defeat more clever block compression attempts, but it will stop naive dedupe of blocks. Default: true. buffer_compress_percentage=int If this is set, then fio will attempt to provide I/O buffer content (on WRITEs) that compresses to the specified level. Fio does this by providing a mix of random data and a fixed pattern. The fixed pattern is either zeros, or the pattern speci‐ fied by buffer_pattern. If the pattern option is used, it might skew the compres‐ sion ratio slightly. Note that this is per block size unit, for file/disk wide com‐ pression level that matches this setting, you'll also want to set refill_buffers. buffer_compress_chunk=int See buffer_compress_percentage. This setting allows fio to manage how big the ranges of random data and zeroed data is. Without this set, fio will provide buf‐ fer_compress_percentage of blocksize random data, followed by the remaining zeroed. With this set to some chunk size smaller than the block size, fio can alternate random and zeroed data throughout the I/O buffer. buffer_pattern=str If set, fio will fill the I/O buffers with this pattern or with the contents of a file. If not set, the contents of I/O buffers are defined by the other options related to buffer contents. The setting can be any pattern of bytes, and can be prefixed with 0x for hex values. It may also be a string, where the string must then be wrapped with "". Or it may also be a filename, where the filename must be wrapped with '' in which case the file is opened and read. Note that not all the file contents will be read if that would cause the buffers to overflow. So, for example: buffer_pattern='filename' or: buffer_pattern="abcd" or: buffer_pattern=-12 or: buffer_pattern=0xdeadface Also you can combine everything together in any order: buffer_pattern=0xdeadface"abcd"-12'filename' dedupe_percentage=int If set, fio will generate this percentage of identical buffers when writing. These buffers will be naturally dedupable. The contents of the buffers depend on what other buffer compression settings have been set. It's possible to have the individ‐ ual buffers either fully compressible, or not at all. This option only controls the distribution of unique buffers. invalidate=bool Invalidate the buffer/page cache parts of the files to be used prior to starting I/O if the platform and file type support it. Defaults to true. This will be ignored if pre_read is also specified for the same job. sync=bool Use synchronous I/O for buffered writes. For the majority of I/O engines, this means using O_SYNC. Default: false. iomem=str, mem=str Fio can use various types of memory as the I/O unit buffer. The allowed values are: malloc Use memory from malloc(3) as the buffers. Default memory type. shm Use shared memory as the buffers. Allocated through shmget(2). shmhuge Same as shm, but use huge pages as backing. mmap Use mmap(2) to allocate buffers. May either be anonymous memory, or can be file backed if a filename is given after the option. The for‐ mat is `mem=mmap:/path/to/file'. mmaphuge Use a memory mapped huge file as the buffer backing. Append filename after mmaphuge, ala `mem=mmaphuge:/hugetlbfs/file'. mmapshared Same as mmap, but use a MMAP_SHARED mapping. cudamalloc Use GPU memory as the buffers for GPUDirect RDMA benchmark. The ioengine must be rdma. The area allocated is a function of the maximum allowed bs size for the job, multi‐ plied by the I/O depth given. Note that for shmhuge and mmaphuge to work, the sys‐ tem must have free huge pages allocated. This can normally be checked and set by reading/writing `/proc/sys/vm/nr_hugepages' on a Linux system. Fio assumes a huge page is 4MiB in size. So to calculate the number of huge pages you need for a given job file, add up the I/O depth of all jobs (normally one unless iodepth is used) and multiply by the maximum bs set. Then divide that number by the huge page size. You can see the size of the huge pages in `/proc/meminfo'. If no huge pages are allocated by having a non-zero number in `nr_hugepages', using mmaphuge or shmhuge will fail. Also see hugepage-size. mmaphuge also needs to have hugetlbfs mounted and the file location should point there. So if it's mounted in `/huge', you would use `mem=mmaphuge:/huge/somefile'. iomem_align=int, mem_align=int This indicates the memory alignment of the I/O memory buffers. Note that the given alignment is applied to the first I/O unit buffer, if using iodepth the alignment of the following buffers are given by the bs used. In other words, if using a bs that is a multiple of the page sized in the system, all buffers will be aligned to this value. If using a bs that is not page aligned, the alignment of subsequent I/O memory buffers is the sum of the iomem_align and bs used. hugepage-size=int Defines the size of a huge page. Must at least be equal to the system setting, see `/proc/meminfo'. Defaults to 4MiB. Should probably always be a multiple of megabytes, so using `hugepage-size=Xm' is the preferred way to set this to avoid setting a non-pow-2 bad value. lockmem=int Pin the specified amount of memory with mlock(2). Can be used to simulate a smaller amount of memory. The amount specified is per worker. I/O size size=int The total size of file I/O for each thread of this job. Fio will run until this many bytes has been transferred, unless runtime is limited by other options (such as runtime, for instance, or increased/decreased by io_size). Fio will divide this size between the available files determined by options such as nrfiles, filename, unless filesize is specified by the job. If the result of division happens to be 0, the size is set to the physical size of the given files or devices if they exist. If this option is not specified, fio will use the full size of the given files or devices. If the files do not exist, size must be given. It is also possible to give size as a percentage between 1 and 100. If `size=20%' is given, fio will use 20% of the full size of the given files or devices. Can be combined with offset to con‐ strain the start and end range that I/O will be done within. io_size=int, io_limit=int Normally fio operates within the region set by size, which means that the size option sets both the region and size of I/O to be performed. Sometimes that is not what you want. With this option, it is possible to define just the amount of I/O that fio should do. For instance, if size is set to 20GiB and io_size is set to 5GiB, fio will perform I/O within the first 20GiB but exit when 5GiB have been done. The opposite is also possible -- if size is set to 20GiB, and io_size is set to 40GiB, then fio will do 40GiB of I/O within the 0..20GiB region. filesize=irange(int) Individual file sizes. May be a range, in which case fio will select sizes for files at random within the given range and limited to size in total (if that is given). If not given, each created file is the same size. This option overrides size in terms of file size, which means this value is used as a fixed size or pos‐ sible range of each file. file_append=bool Perform I/O after the end of the file. Normally fio will operate within the size of a file. If this option is set, then fio will append to the file instead. This has identical behavior to setting offset to the size of a file. This option is ignored on non-regular files. fill_device=bool, fill_fs=bool Sets size to something really large and waits for ENOSPC (no space left on device) as the terminating condition. Only makes sense with sequential write. For a read workload, the mount point will be filled first then I/O started on the result. This option doesn't make sense if operating on a raw device node, since the size of that is already known by the file system. Additionally, writing beyond end-of-device will not return ENOSPC there. I/O engine ioengine=str Defines how the job issues I/O to the file. The following types are defined: sync Basic read(2) or write(2) I/O. lseek(2) is used to position the I/O location. See fsync and fdatasync for syncing write I/Os. psync Basic pread(2) or pwrite(2) I/O. Default on all supported operating systems except for Windows. vsync Basic readv(2) or writev(2) I/O. Will emulate queuing by coalescing adjacent I/Os into a single submission. pvsync Basic preadv(2) or pwritev(2) I/O. pvsync2 Basic preadv2(2) or pwritev2(2) I/O. libaio Linux native asynchronous I/O. Note that Linux may only support queued behavior with non-buffered I/O (set `direct=1' or `buffered=0'). This engine defines engine specific options. posixaio POSIX asynchronous I/O using aio_read(3) and aio_write(3). solarisaio Solaris native asynchronous I/O. windowsaio Windows native asynchronous I/O. Default on Windows. mmap File is memory mapped with mmap(2) and data copied to/from using mem‐ cpy(3). splice splice(2) is used to transfer the data and vmsplice(2) to transfer data from user space to the kernel. sg SCSI generic sg v3 I/O. May either be synchronous using the SG_IO ioctl, or if the target is an sg character device we use read(2) and write(2) for asynchronous I/O. Requires filename option to specify either block or character devices. null Doesn't transfer any data, just pretends to. This is mainly used to exercise fio itself and for debugging/testing purposes. net Transfer over the network to given `host:port'. Depending on the pro‐ tocol used, the hostname, port, listen and filename options are used to specify what sort of connection to make, while the protocol option determines which protocol will be used. This engine defines engine specific options. netsplice Like net, but uses splice(2) and vmsplice(2) to map data and send/receive. This engine defines engine specific options. cpuio Doesn't transfer any data, but burns CPU cycles according to the cpu‐ load and cpuchunks options. Setting cpuload=85 will cause that job to do nothing but burn 85% of the CPU. In case of SMP machines, use `numjobs=<nr_of_cpu>' to get desired CPU usage, as the cpuload only loads a single CPU at the desired rate. A job never finishes unless there is at least one non-cpuio job. guasi The GUASI I/O engine is the Generic Userspace Asyncronous Syscall Interface approach to async I/O. See for more info on GUASI. rdma The RDMA I/O engine supports both RDMA memory semantics (RDMA_WRITE/RDMA_READ) and channel semantics (Send/Recv) for the InfiniBand, RoCE and iWARP protocols. falloc I/O engine that does regular fallocate to simulate data transfer as fio ioengine. DDIR_READ does fallocate(,mode = FALLOC_FL_KEEP_SIZE,). DIR_WRITE does fallocate(,mode = 0). DDIR_TRIM does fallocate(,mode = FALLOC_FL_KEEP_SIZE|FAL‐ LOC_FL_PUNCH_HOLE). ftruncate I/O engine that sends ftruncate(2) operations in response to write (DDIR_WRITE) events. Each ftruncate issued sets the file's size to the current block offset. blocksize is ignored. e4defrag I/O engine that does regular EXT4_IOC_MOVE_EXT ioctls to simulate defragment activity in request to DDIR_WRITE event. rbd I/O engine supporting direct access to Ceph Rados Block Devices (RBD) via librbd without the need to use the kernel rbd driver. This ioengine defines engine specific options. gfapi Using GlusterFS libgfapi sync interface to direct access to GlusterFS volumes without having to go through FUSE. This ioengine defines engine specific options. gfapi_async Using GlusterFS libgfapi async interface to direct access to Glus‐ terFS volumes without having to go through FUSE. This ioengine defines engine specific options. libhdfs Read and write through Hadoop (HDFS). The filename option is used to specify host,port of the hdfs name-node to connect. This engine interprets offsets a little differently. In HDFS, files once created cannot be modified so random writes are not possible. To imitate this the libhdfs engine expects a bunch of small files to be created over HDFS and will randomly pick a file from them based on the offset gen‐ erated by fio backend (see the example job file to create such files, use `rw=write' option). Please note, it may be necessary to set envi‐ ronment variables to work with HDFS/libhdfs properly. Each job uses its own connection to HDFS. mtd Read, write and erase an MTD character device (e.g., `/dev/mtd0'). Discards are treated as erases. Depending on the underlying device type, the I/O may have to go in a certain pattern, e.g., on NAND, writing sequentially to erase blocks and discarding before overwrit‐ ing. The trimwrite mode works well for this constraint. pmemblk Read and write using filesystem DAX to a file on a filesystem mounted with DAX on a persistent memory device through the NVML libpmemblk library. dev-dax Read and write using device DAX to a persistent memory device (e.g., /dev/dax0.0) through the NVML libpmem library. external Prefix to specify loading an external I/O engine object file. Append the engine filename, e.g. `ioengine=external:/tmp/foo.o' to load ioengine `foo.o' in `/tmp'. The path can be either absolute or rela‐ tive. See `engines/skeleton_external.c' in the fio source for details of writing an external I/O engine. I/O engine specific parameters In addition, there are some parameters which are only valid when a specific ioengine is in use. These are used identically to normal parameters, with the caveat that when used on the command line, they must come after the ioengine that defines them is selected. (libaio)userspace_reap Normally, with the libaio engine in use, fio will use the io_getevents(3) system call to reap newly returned events. With this flag turned on, the AIO ring will be read directly from user-space to reap events. The reaping mode is only enabled when polling for a minimum of 0 events (e.g. when `iodepth_batch_complete=0'). (pvsync2)hipri Set RWF_HIPRI on I/O, indicating to the kernel that it's of higher priority than normal. (pvsync2)hipri_percentage When hipri is set this determines the probability of a pvsync2 I/O being high pri‐ ority. The default is 100%. (cpuio)cpuload=int Attempt to use the specified percentage of CPU cycles. This is a mandatory option when using cpuio I/O engine. (cpuio)cpuchunks=int Split the load into cycles of the given time. In microseconds. (cpuio)exit_on_io_done=bool Detect when I/O threads are done, then exit. (libhdfs)namenode=str The hostname or IP address of a HDFS cluster namenode to contact. (libhdfs)port The listening port of the HFDS cluster namenode. (netsplice,net)port The TCP or UDP port to bind to or connect to. If this is used with numjobs to spawn multiple instances of the same job type, then this will be the starting port number since fio will use a range of ports. (netsplice,net)hostname=str The hostname or IP address to use for TCP or UDP based I/O. If the job is a TCP listener or UDP reader, the hostname is not used and must be omitted unless it is a valid UDP multicast address. (netsplice,net)interface=str The IP address of the network interface used to send or receive UDP multicast. (netsplice,net)ttl=int Time-to-live value for outgoing UDP multicast packets. Default: 1. (netsplice,net)nodelay=bool Set TCP_NODELAY on TCP connections. (netsplice,net)protocol=str, proto=str The network protocol to use. Accepted values are: tcp Transmission control protocol. tcpv6 Transmission control protocol V6. udp User datagram protocol. udpv6 User datagram protocol V6. unix UNIX domain socket. When the protocol is TCP or UDP, the port must also be given, as well as the host‐ name if the job is a TCP listener or UDP reader. For unix sockets, the normal file‐ name option should be used and the port is invalid. (netsplice,net)listen For TCP network connections, tell fio to listen for incoming connections rather than initiating an outgoing connection. The hostname must be omitted if this option is used. (netsplice,net)pingpong Normally a network writer will just continue writing data, and a network reader will just consume packages. If `pingpong=1' is set, a writer will send its normal payload to the reader, then wait for the reader to send the same payload back. This allows fio to measure network latencies. The submission and completion latencies then measure local time spent sending or receiving, and the completion latency mea‐ sures how long it took for the other end to receive and send back. For UDP multi‐ cast traffic `pingpong=1' should only be set for a single reader when multiple readers are listening to the same address. (netsplice,net)window_size=int Set the desired socket buffer size for the connection. (netsplice,net)mss=int Set the TCP maximum segment size (TCP_MAXSEG). (e4defrag)donorname=str File will be used as a block donor (swap extents between files). (e4defrag)inplace=int Configure donor file blocks allocation strategy: 0 Default. Preallocate donor's file on init. 1 Allocate space immediately inside defragment event, and free right after event. (rbd)clustername=str Specifies the name of the Ceph cluster. (rbd)rbdname=str Specifies the name of the RBD. (rbd)pool=str Specifies the name of the Ceph pool containing RBD. (rbd)clientname=str Specifies the username (without the 'client.' prefix) used to access the Ceph clus‐ ter. If the clustername is specified, the clientname shall be the full ** string. If no type. prefix is given, fio will add 'client.' by default. (mtd)skip_bad=bool Skip operations against known bad blocks. (libhdfs)hdfsdirectory libhdfs will create chunk in this HDFS directory. (libhdfs)chunk_size The size of the chunk to use for each file. I/O depth iodepth=int Number of I/O units to keep in flight against the file. Note that increasing iodepth beyond 1 will not affect synchronous ioengines (except for small degrees when verify_async is in use). Even async engines may impose OS restrictions causing the desired depth not to be achieved. This may happen on Linux when using libaio and not setting `direct=1', since buffered I/O is not async on that OS. Keep an eye on the I/O depth distribution in the fio output to verify that the achieved depth is as expected. Default: 1. iodepth_batch_submit=int, iodepth_batch=int This defines how many pieces of I/O to submit at once. It defaults to 1 which means that we submit each I/O as soon as it is available, but can be raised to submit bigger batches of I/O at the time. If it is set to 0 the iodepth value will be used. iodepth_batch_complete_min=int, iodepth_batch_complete=int This defines how many pieces of I/O to retrieve at once. It defaults to 1 which means that we'll ask for a minimum of 1 I/O in the retrieval process from the ker‐ nel. The I/O retrieval will go on until we hit the limit set by iodepth_low. If this variable is set to 0, then fio will always check for completed events before queuing more I/O. This helps reduce I/O latency, at the cost of more retrieval sys‐ tem calls. iodepth_batch_complete_max=int This defines maximum pieces of I/O to retrieve at once. This variable should be used along with iodepth_batch_complete_min=int variable, specifying the range of min and max amount of I/O which should be retrieved. By default it is equal to iodepth_batch_complete_min value. Example #1: iodepth_batch_complete_min=1 iodepth_batch_complete_max=<iodepth> which means that we will retrieve at least 1 I/O and up to the whole submitted queue depth. If none of I/O has been completed yet, we will wait. Example #2: iodepth_batch_complete_min=0 iodepth_batch_complete_max=<iodepth> which means that we can retrieve up to the whole submitted queue depth, but if none of I/O has been completed yet, we will NOT wait and immediately exit the system call. In this example we simply do polling. iodepth_low=int The low water mark indicating when to start filling the queue again. Defaults to the same as iodepth, meaning that fio will attempt to keep the queue full at all times. If iodepth is set to e.g. 16 and iodepth_low is set to 4, then after fio has filled the queue of 16 requests, it will let the depth drain down to 4 before starting to fill it again. serialize_overlap=bool Serialize in-flight I/Os that might otherwise cause or suffer from data races. When two or more I/Os are submitted simultaneously, there is no guarantee that the I/Os will be processed or completed in the submitted order. Further, if two or more of those I/Os are writes, any overlapping region between them can become indetermi‐ nate/undefined on certain storage. These issues can cause verification to fail erratically when at least one of the racing I/Os is changing data and the overlap‐ ping region has a non-zero size. Setting serialize_overlap tells fio to avoid pro‐ voking this behavior by explicitly serializing in-flight I/Os that have a non-zero overlap. Note that setting this option can reduce both performance and the iodepth achieved. Additionally this option does not work when io_submit_mode is set to offload. Default: false. io_submit_mode=str This option controls how fio submits the I/O to the I/O engine. The default is `inline', which means that the fio job threads submit and reap I/O directly. If set to `offload', the job threads will offload I/O submission to a dedicated pool of I/O threads. This requires some coordination and thus has a bit of extra overhead, especially for lower queue depth I/O where it can increase latencies. The benefit is that fio can manage submission rates independently of the device completion rates. This avoids skewed latency reporting if I/O gets backed up on the device side (the coordinated omission problem). I/O rate thinktime=time Stall the job for the specified period of time after an I/O has completed before issuing the next. May be used to simulate processing being done by an application. When the unit is omitted, the value is interpreted in microseconds. See think‐ time_blocks and thinktime_spin. thinktime_spin=time Only valid if thinktime is set - pretend to spend CPU time doing something with the data received, before falling back to sleeping for the rest of the period specified by thinktime. When the unit is omitted, the value is interpreted in microseconds. thinktime_blocks=int Only valid if thinktime is set - control how many blocks to issue, before waiting thinktime usecs. If not set, defaults to 1 which will make fio wait thinktime usecs after every block. This effectively makes any queue depth setting redundant, since no more than 1 I/O will be queued before we have to complete it and do our think‐ time. In other words, this setting effectively caps the queue depth if the latter is larger. rate=int[,int][,int] Cap the bandwidth used by this job. The number is in bytes/sec, the normal suffix rules apply. Comma-separated values may be specified for reads, writes, and trims as described in blocksize. For example, using `rate=1m,500k' would limit reads to 1MiB/sec and writes to 500KiB/sec. Capping only reads or writes can be done with `rate=,500k' or `rate=500k,' where the former will only limit writes (to 500KiB/sec) and the latter will only limit reads. rate_min=int[,int][,int] Tell fio to do whatever it can to maintain at least this bandwidth. Failing to meet this requirement will cause the job to exit. Comma-separated values may be speci‐ fied for reads, writes, and trims as described in blocksize. rate_iops=int[,int][,int] Cap the bandwidth to this number of IOPS. Basically the same as rate, just speci‐ fied independently of bandwidth. If the job is given a block size range instead of a fixed value, the smallest block size is used as the metric. Comma-separated val‐ ues may be specified for reads, writes, and trims as described in blocksize. rate_iops_min=int[,int][,int] If fio doesn't meet this rate of I/O, it will cause the job to exit. Comma-sepa‐ rated values may be specified for reads, writes, and trims as described in block‐ size. rate_process=str This option controls how fio manages rated I/O submissions. The default is `lin‐ ear', which submits I/O in a linear fashion with fixed delays between I/Os that gets adjusted based on I/O completion rates. If this is set to `poisson', fio will submit I/O based on a more real world random request flow, known as the Poisson process ( The lambda will be 10^6 / IOPS for the given workload. I/O latency latency_target=time If set, fio will attempt to find the max performance point that the given workload will run at while maintaining a latency below this target. When the unit is omit‐ ted, the value is interpreted in microseconds. See latency_window and latency_per‐ centile. latency_window=time Used with latency_target to specify the sample window that the job is run at vary‐ ing queue depths to test the performance. When the unit is omitted, the value is interpreted in microseconds. latency_percentile=float The percentage of I/Os that must fall within the criteria specified by latency_tar‐ get and latency_window. If not set, this defaults to 100.0, meaning that all I/Os must be equal or below to the value set by latency_target. max_latency=time If set, fio will exit the job with an ETIMEDOUT error if it exceeds this maximum latency. When the unit is omitted, the value is interpreted in microseconds. rate_cycle=int Average bandwidth for rate and rate_min over this number of milliseconds. Defaults to 1000. I/O replay write_iolog=str Write the issued I/O patterns to the specified file. See read_iolog. Specify a sep‐ arate file for each job, otherwise the iologs will be interspersed and the file may be corrupt. read_iolog=str Open an iolog with the specified filename and replay the I/O patterns it contains. This can be used to store a workload and replay it sometime later. The iolog given may also be a blktrace binary file, which allows fio to replay a workload captured by blktrace. See blktrace(8) for how to capture such logging data. For blktrace replay, the file needs to be turned into a blkparse binary data file first (`blk‐ parse <device> -o /dev/null -d file_for_fio.bin'). replay_no_stall=bool When replaying I/O with read_iolog the default behavior is to attempt to respect the timestamps within the log and replay them with the appropriate delay between IOPS. By setting this variable fio will not respect the timestamps and attempt to replay them as fast as possible while still respecting ordering. The result is the same I/O pattern to a given device, but different timings. replay_redirect=str While replaying I/O patterns using read_iolog the default behavior is to replay the IOPS onto the major/minor device that each IOP was recorded from. This is sometimes undesirable because on a different machine those major/minor numbers can map to a different device. Changing hardware on the same system can also result in a differ‐ ent major/minor mapping. replay_redirect causes all I/Os to be replayed onto the single specified device regardless of the device it was recorded from. i.e. `replay_redirect=/dev/sdc' would cause all I/O in the blktrace or iolog to be replayed onto `/dev/sdc'. This means multiple devices will be replayed onto a sin‐ gle device, if the trace contains multiple devices. If you want multiple devices to be replayed concurrently to multiple redirected devices you must blkparse your trace into separate traces and replay them with independent fio invocations. Unfortunately this also breaks the strict time ordering between multiple device accesses. replay_align=int Force alignment of I/O offsets and lengths in a trace to this power of 2 value. replay_scale=int Scale sector offsets down by this factor when replaying traces. Threads, processes and job synchronization thread Fio defaults to creating jobs by using fork, however if this option is given, fio will create jobs by using POSIX Threads' function pthread_create(3) to create threads instead. wait_for=str If set, the current job won't be started until all workers of the specified waitee job are done. wait_for operates on the job name basis, so there are a few limita‐ tions. First, the waitee must be defined prior to the waiter job (meaning no for‐ ward references). Second, if a job is being referenced as a waitee, it must have a unique name (no duplicate waitees). nice=int Run the job with the given nice value. See man nice(2). On Windows, values less than -15 set the process class to "High"; -1 through -15 set "Above Normal"; 1 through 15 "Below Normal"; and above 15 "Idle" priority class. prio=int Set the I/O priority value of this job. Linux limits us to a positive value between 0 and 7, with 0 being the highest. See man ionice(1). Refer to an appropriate man‐ page for other operating systems since meaning of priority may differ. prioclass=int Set the I/O priority class. See man ionice(1). cpumask=int Set the CPU affinity of this job. The parameter given is a bit mask of allowed CPUs the job may run on. So if you want the allowed CPUs to be 1 and 5, you would pass the decimal value of (1 << 1 | 1 << 5), or 34. See man sched_setaffinity(2). This may not work on all supported operating systems or kernel versions. This option doesn't work well for a higher CPU count than what you can store in an integer mask, so it can only control cpus 1-32. For boxes with larger CPU counts, use cpus_allowed. cpus_allowed=str Controls the same options as cpumask, but accepts a textual specification of the permitted CPUs instead. So to use CPUs 1 and 5 you would specify `cpus_allowed=1,5'. This option also allows a range of CPUs to be specified -- say you wanted a binding to CPUs 1, 5, and 8 to 15, you would set `cpus_allowed=1,5,8-15'. cpus_allowed_policy=str Set the policy of how fio distributes the CPUs specified by cpus_allowed or cpumask. Two policies are supported: shared All jobs will share the CPU set specified. split Each job will get a unique CPU from the CPU set. shared is the default behavior, if the option isn't specified. If split is speci‐ fied, then fio will will assign one cpu per job. If not enough CPUs are given for the jobs listed, then fio will roundrobin the CPUs in the set. numa_cpu_nodes=str Set this job running on specified NUMA nodes' CPUs. The arguments allow comma delimited list of cpu numbers, A-B ranges, or `all'. Note, to enable NUMA options support, fio must be built on a system with libnuma-dev(el) installed. numa_mem_policy=str Set this job's memory policy and corresponding NUMA nodes. Format of the arguments: <mode>[:<nodelist>] `mode' is one of the following memory poicies: `default', `prefer', `bind', `inter‐ leave' or `local'. For `default' and `local' memory policies, no node needs to be specified. For `prefer', only one node is allowed. For `bind' and `interleave' the `nodelist' may be as follows: a comma delimited list of numbers, A-B ranges, or `all'. cgroup=str Add job to this control group. If it doesn't exist, it will be created. The system must have a mounted cgroup blkio mount point for this to work. If your system doesn't have it mounted, you can do so with: # mount -t cgroup -o blkio none /cgroup cgroup_weight=int Set the weight of the cgroup to this value. See the documentation that comes with the kernel, allowed values are in the range of 100..1000. cgroup_nodelete=bool Normally fio will delete the cgroups it has created after the job completion. To override this behavior and to leave cgroups around after the job completion, set `cgroup_nodelete=1'. This can be useful if one wants to inspect various cgroup files after job completion. Default: false. flow_id=int The ID of the flow. If not specified, it defaults to being a global flow. See flow. flow=int Weight in token-based flow control. If this value is used, then there is a 'flow counter' which is used to regulate the proportion of activity between two or more jobs. Fio attempts to keep this flow counter near zero. The flow parameter stands for how much should be added or subtracted to the flow counter on each iteration of the main I/O loop. That is, if one job has `flow=8' and another job has `flow=-1', then there will be a roughly 1:8 ratio in how much one runs vs the other. flow_watermark=int The maximum value that the absolute value of the flow counter is allowed to reach before the job must wait for a lower value of the counter. flow_sleep=int The period of time, in microseconds, to wait after the flow watermark has been exceeded before retrying operations. stonewall, wait_for_previous Wait for preceding jobs in the job file to exit, before starting this one. Can be used to insert serialization points in the job file. A stone wall also implies starting a new reporting group, see group_reporting. exitall By default, fio will continue running all other jobs when one job finishes but sometimes this is not the desired action. Setting exitall will instead make fio terminate all other jobs when one job finishes. exec_prerun=str Before running this job, issue the command specified through system(3). Output is redirected in a file called `jobname.prerun.txt'. exec_postrun=str After the job completes, issue the command specified though system(3). Output is redirected in a file called `jobname.postrun.txt'. uid=int Instead of running as the invoking user, set the user ID to this value before the thread/process does any work. gid=int Set group ID, see uid. Verification verify_only Do not perform specified workload, only verify data still matches previous invoca‐ tion of this workload. This option allows one to check data multiple times at a later date without overwriting it. This option makes sense only for workloads that write data, and does not support workloads with the time_based option set. do_verify=bool Run the verify phase after a write phase. Only valid if verify is set. Default: true. verify=str If writing to a file, fio can verify the file contents after each iteration of the job. Each verification method also implies verification of special header, which is written to the beginning of each block. This header also includes meta information, like offset of the block, block number, timestamp when block was written, etc. ver‐ ify can be combined with verify_pattern option. The allowed values are: md5 Use an md5 sum of the data area and store it in the header of each block. crc64 Use an experimental crc64 sum of the data area and store it in the header of each block. crc32c Use a crc32c sum of the data area and store it in the header of each block. This will automatically use hardware acceleration (e.g. SSE4.2 on an x86 or CRC crypto extensions on ARM64) but will fall back to software crc32c if none is found. Generally the fatest checksum fio supports when hardware accelerated. crc32c-intel Synonym for crc32c. crc32 Use a crc32 sum of the data area and store it in the header of each block. crc16 Use a crc16 sum of the data area and store it in the header of each block. crc7 Use a crc7 sum of the data area and store it in the header of each block. xxhash Use xxhash as the checksum function. Generally the fastest software checksum that fio supports. sha512 Use sha512 as the checksum function. sha256 Use sha256 as the checksum function. sha1 Use optimized sha1 as the checksum function. sha3-224 Use optimized sha3-224 as the checksum function. sha3-256 Use optimized sha3-256 as the checksum function. sha3-384 Use optimized sha3-384 as the checksum function. sha3-512 Use optimized sha3-512 as the checksum function. meta This option is deprecated, since now meta information is included in generic verification header and meta verification happens by default. For detailed information see the description of the verify setting. This option is kept because of compatibility's sake with old configu‐ rations. Do not use it. pattern Verify a strict pattern. Normally fio includes a header with some basic information and checksumming, but if this option is set, only the specific pattern set with verify_pattern is verified. null Only pretend to verify. Useful for testing internals with `ioengine=null', not for much else. This option can be used for repeated burn-in tests of a system to make sure that the written data is also correctly read back. If the data direction given is a read or random read, fio will assume that it should verify a previously written file. If the data direction includes any form of write, the verify will be of the newly written data. verifysort=bool If true, fio will sort written verify blocks when it deems it faster to read them back in a sorted manner. This is often the case when overwriting an existing file, since the blocks are already laid out in the file system. You can ignore this option unless doing huge amounts of really fast I/O where the red-black tree sort‐ ing CPU time becomes significant. Default: true. verifysort_nr=int Pre-load and sort verify blocks for a read workload. verify_offset=int Swap the verification header with data somewhere else in the block before writing. It is swapped back before verifying. verify_interval=int Write the verification header at a finer granularity than the blocksize. It will be written for chunks the size of verify_interval. blocksize should divide this evenly. verify_pattern=str If set, fio will fill the I/O buffers with this pattern. Fio defaults to filling with totally random bytes, but sometimes it's interesting to fill with a known pat‐ tern for I/O verification purposes. Depending on the width of the pattern, fio will fill 1/2/3/4 bytes of the buffer at the time (it can be either a decimal or a hex number). The verify_pattern if larger than a 32-bit quantity has to be a hex number that starts with either "0x" or "0X". Use with verify. Also, verify_pattern sup‐ ports %o format, which means that for each block offset will be written and then verified back, e.g.: verify_pattern=%o Or use combination of everything: verify_pattern=0xff%o"abcd"-12 verify_fatal=bool Normally fio will keep checking the entire contents before quitting on a block ver‐ ification failure. If this option is set, fio will exit the job on the first observed failure. Default: false. verify_dump=bool If set, dump the contents of both the original data block and the data block we read off disk to files. This allows later analysis to inspect just what kind of data corruption occurred. Off by default. verify_async=int Fio will normally verify I/O inline from the submitting thread. This option takes an integer describing how many async offload threads to create for I/O verification instead, causing fio to offload the duty of verifying I/O contents to one or more separate threads. If using this offload option, even sync I/O engines can benefit from using an iodepth setting higher than 1, as it allows them to have I/O in flight while verifies are running. Defaults to 0 async threads, i.e. verification is not asynchronous. verify_async_cpus=str Tell fio to set the given CPU affinity on the async I/O verification threads. See cpus_allowed for the format used. verify_backlog=int Fio will normally verify the written contents of a job that utilizes verify once that job has completed. In other words, everything is written then everything is read back and verified. You may want to verify continually instead for a variety of reasons. Fio stores the meta data associated with an I/O block in memory, so for large verify workloads, quite a bit of memory would be used up holding this meta data. If this option is enabled, fio will write only N blocks before verifying these blocks. verify_backlog_batch=int Control how many blocks fio will verify if verify_backlog is set. If not set, will default to the value of verify_backlog (meaning the entire queue is read back and verified). If verify_backlog_batch is less than verify_backlog then not all blocks will be verified, if verify_backlog_batch is larger than verify_backlog, some blocks will be verified more than once. verify_state_save=bool When a job exits during the write phase of a verify workload, save its current state. This allows fio to replay up until that point, if the verify state is loaded for the verify read phase. The format of the filename is, roughly: <type>-<jobname>-<jobindex>-verify.state. <type> is "local" for a local run, "sock" for a client/server socket connection, and "ip" (, for instance) for a networked client/server connection. Defaults to true. verify_state_load=bool If a verify termination trigger was used, fio stores the current write state of each thread. This can be used at verification time so that fio knows how far it should verify. Without this information, fio will run a full verification pass, according to the settings in the job file used. Default false. trim_percentage=int Number of verify blocks to discard/trim. trim_verify_zero=bool Verify that trim/discarded blocks are returned as zeros. trim_backlog=int Verify that trim/discarded blocks are returned as zeros. trim_backlog_batch=int Trim this number of I/O blocks. experimental_verify=bool Enable experimental verification. Steady state steadystate=str:float, ss=str:float Define the criterion and limit for assessing steady state performance. The first parameter designates the criterion whereas the second parameter sets the threshold. When the criterion falls below the threshold for the specified duration, the job will stop. For example, `iops_slope:0.1%' will direct fio to terminate the job when the least squares regression slope falls below 0.1% of the mean IOPS. If group_reporting is enabled this will apply to all jobs in the group. Below is the list of available steady state assessment criteria. All assessments are carried out using only data from the rolling collection window. Threshold limits can be expressed as a fixed value or as a percentage of the mean in the collection window. iops Collect IOPS data. Stop the job if all individual IOPS measurements are within the specified limit of the mean IOPS (e.g., `iops:2' means that all individual IOPS values must be within 2 of the mean, whereas `iops:0.2%' means that all individual IOPS values must be within 0.2% of the mean IOPS to terminate the job). iops_slope Collect IOPS data and calculate the least squares regression slope. Stop the job if the slope falls below the specified limit. bw Collect bandwidth data. Stop the job if all individual bandwidth mea‐ surements are within the specified limit of the mean bandwidth. bw_slope Collect bandwidth data and calculate the least squares regression slope. Stop the job if the slope falls below the specified limit. steadystate_duration=time, ss_dur=time A rolling window of this duration will be used to judge whether steady state has been reached. Data will be collected once per second. The default is 0 which dis‐ ables steady state detection. When the unit is omitted, the value is interpreted in seconds. steadystate_ramp_time=time, ss_ramp=time Allow the job to run for the specified duration before beginning data collection for checking the steady state job termination criterion. The default is 0. When the unit is omitted, the value is interpreted in seconds. Measurements and reporting per_job_logs=bool If set, this generates bw/clat/iops log with per file private filenames. If not set, jobs with identical names will share the log filename. Default: true. group_reporting It may sometimes be interesting to display statistics for groups of jobs as a whole instead of for each individual job. This is especially true if numjobs is used; looking at individual thread/process output quickly becomes unwieldy. To see the final report per-group instead of per-job, use group_reporting. Jobs in a file will be part of the same reporting group, unless if separated by a stonewall, or by using new_group. new_group Start a new reporting group. See: group_reporting. If not given, all jobs in a file will be part of the same reporting group, unless separated by a stonewall. stats=bool By default, fio collects and shows final output results for all jobs that run. If this option is set to 0, then fio will ignore it in the final stat output. write_bw_log=str If given, write a bandwidth log for this job. Can be used to store data of the bandwidth of the jobs in their lifetime. The included fio_generate_plots script uses gnuplot to turn these text files into nice graphs. See write_lat_log for behavior of given filename. For this option, the postfix is `_bw.x.log', where `x' is the index of the job (1..N, where N is the number of jobs). If per_job_logs is false, then the filename will not include the job index. See LOG FILE FORMATS sec‐ tion. write_lat_log=str Same as write_bw_log, except that this option stores I/O submission, completion, and total latencies instead. If no filename is given with this option, the default filename of `jobname_type.log' is used. Even if the filename is given, fio will still append the type of log. So if one specifies: write_lat_log=foo The actual log names will be `foo_slat.x.log', `foo_clat.x.log', and `foo_lat.x.log', where `x' is the index of the job (1..N, where N is the number of jobs). This helps fio_generate_plots find the logs automatically. If per_job_logs is false, then the filename will not include the job index. See LOG FILE FORMATS section. write_hist_log=str Same as write_lat_log, but writes I/O completion latency histograms. If no filename is given with this option, the default filename of `jobname_clat_hist.x.log' is used, where `x' is the index of the job (1..N, where N is the number of jobs). Even if the filename is given, fio will still append the type of log. If per_job_logs is false, then the filename will not include the job index. See LOG FILE FORMATS sec‐ tion. write_iops_log=str Same as write_bw_log, but writes IOPS. If no filename is given with this option, the default filename of `jobname_type.x.log' is used, where `x' is the index of the job (1..N, where N is the number of jobs). Even if the filename is given, fio will still append the type of log. If per_job_logs is false, then the filename will not include the job index. See LOG FILE FORMATS section. log_avg_msec=int By default, fio will log an entry in the iops, latency, or bw log for every I/O that completes. When writing to the disk log, that can quickly grow to a very large size. Setting this option makes fio average the each log entry over the specified period of time, reducing the resolution of the log. See log_max_value as well. Defaults to 0, logging all entries. Also see LOG FILE FORMATS section. log_hist_msec=int Same as log_avg_msec, but logs entries for completion latency histograms. Computing latency percentiles from averages of intervals using log_avg_msec is inaccurate. Setting this option makes fio log histogram entries over the specified period of time, reducing log sizes for high IOPS devices while retaining percentile accuracy. See log_hist_coarseness as well. Defaults to 0, meaning histogram logging is dis‐ abled. log_hist_coarseness=int Integer ranging from 0 to 6, defining the coarseness of the resolution of the his‐ togram logs enabled with log_hist_msec. For each increment in coarseness, fio out‐ puts half as many bins. Defaults to 0, for which histogram logs contain 1216 latency bins. See LOG FILE FORMATS section. log_max_value=bool If log_avg_msec is set, fio logs the average over that window. If you instead want to log the maximum value, set this option to 1. Defaults to 0, meaning that aver‐ aged values are logged. log_offset=bool If this is set, the iolog options will include the byte offset for the I/O entry as well as the other data values. Defaults to 0 meaning that offsets are not present in logs. Also see LOG FILE FORMATS section. log_compression=int If this is set, fio will compress the I/O logs as it goes, to keep the memory foot‐ print lower. When a log reaches the specified size, that chunk is removed and com‐ pressed in the background. Given that I/O logs are fairly highly compressible, this yields a nice memory savings for longer runs. The downside is that the compression will consume some background CPU cycles, so it may impact the run. This, however, is also true if the logging ends up consuming most of the system memory. So pick your poison. The I/O logs are saved normally at the end of a run, by decompressing the chunks and storing them in the specified log file. This feature depends on the availability of zlib. log_compression_cpus=str Define the set of CPUs that are allowed to handle online log compression for the I/O jobs. This can provide better isolation between performance sensitive jobs, and background compression work. log_store_compressed=bool If set, fio will store the log files in a compressed format. They can be decom‐ pressed with fio, using the --inflate-log command line parameter. The files will be stored with a `.fz' suffix. log_unix_epoch=bool If set, fio will log Unix timestamps to the log files produced by enabling write_type_log for each log type, instead of the default zero-based timestamps. block_error_percentiles=bool If set, record errors in trim block-sized units from writes and trims and output a histogram of how many trims it took to get to errors, and what kind of error was encountered. bwavgtime=int Average the calculated bandwidth over the given time. Value is specified in mil‐ liseconds. If the job also does bandwidth logging through write_bw_log, then the minimum of this option and log_avg_msec will be used. Default: 500ms. iopsavgtime=int Average the calculated IOPS over the given time. Value is specified in millisec‐ onds. If the job also does IOPS logging through write_iops_log, then the minimum of this option and log_avg_msec will be used. Default: 500ms. disk_util=bool Generate disk utilization statistics, if the platform supports it. Default: true. disable_lat=bool Disable measurements of total latency numbers. Useful only for cutting back the number of calls to gettimeofday(2), as that does impact performance at really high IOPS rates. Note that to really get rid of a large amount of these calls, this option must be used with disable_slat and disable_bw_measurement as well. disable_clat=bool Disable measurements of completion latency numbers. See disable_lat. disable_slat=bool Disable measurements of submission latency numbers. See disable_lat. disable_bw_measurement=bool, disable_bw=bool Disable measurements of throughput/bandwidth numbers. See disable_lat. clat_percentiles=bool Enable the reporting of percentiles of completion latencies. This option is mutu‐ ally exclusive with lat_percentiles. lat_percentiles=bool Enable the reporting of percentiles of IO latencies. This is similar to clat_per‐ centiles, except that this includes the submission latency. This option is mutu‐ ally exclusive with clat_percentiles. percentile_list=float_list Overwrite the default list of percentiles for completion latencies and the block error histogram. Each number is a floating number in the range (0,100], and the maximum length of the list is 20. Use ':' to separate the numbers, and list the numbers in ascending order. For example, `--percentile_list=99.5:99.9' will cause fio to report the values of completion latency below which 99.5% and 99.9% of the observed latencies fell, respectively. Error handling exitall_on_error When one job finishes in error, terminate the rest. The default is to wait for each job to finish. continue_on_error=str Normally fio will exit the job on the first observed failure. If this option is set, fio will continue the job when there is a 'non-fatal error' (EIO or EILSEQ) until the runtime is exceeded or the I/O size specified is completed. If this option is used, there are two more stats that are appended, the total error count and the first error. The error field given in the stats is the first error that was hit during the run. The allowed values are: none Exit on any I/O or verify errors. read Continue on read errors, exit on all others. write Continue on write errors, exit on all others. io Continue on any I/O error, exit on all others. verify Continue on verify errors, exit on all others. all Continue on all errors. 0 Backward-compatible alias for 'none'. 1 Backward-compatible alias for 'all'. ignore_error=str Sometimes you want to ignore some errors during test in that case you can specify error list for each error type, instead of only being able to ignore the default 'non-fatal error' using continue_on_error. `ignore_error=READ_ERR_LIST,WRITE_ERR_LIST,VERIFY_ERR_LIST' errors for given error type is separated with ':'. Error may be symbol ('ENOSPC', 'ENOMEM') or integer. Example: ignore_error=EAGAIN,ENOSPC:122 This option will ignore EAGAIN from READ, and ENOSPC and 122(EDQUOT) from WRITE. This option works by overriding continue_on_error with the list of errors for each error type if any. error_dump=bool If set dump every error even if it is non fatal, true by default. If disabled only fatal error will be dumped. Running predefined workloads Fio includes predefined profiles that mimic the I/O workloads generated by other tools. profile=str The predefined workload to run. Current profiles are: tiobench Threaded I/O bench (tiotest/tiobench) like workload. act Aerospike Certification Tool (ACT) like workload. To view a profile's additional options use --cmdhelp after specifying the profile. For example: $ fio --profile=act --cmdhelp Act profile options device-names=str Devices to use. load=int ACT load multiplier. Default: 1. test-duration=time How long the entire test takes to run. When the unit is omitted, the value is given in seconds. Default: 24h. threads-per-queue=int Number of read I/O threads per device. Default: 8. read-req-num-512-blocks=int Number of 512B blocks to read at the time. Default: 3. large-block-op-kbytes=int Size of large block ops in KiB (writes). Default: 131072. prep Set to run ACT prep phase. Tiobench profile options size=str Size in MiB. block=int Block size in bytes. Default: 4096. numruns=int Number of runs. dir=str Test directory. threads=int Number of threads.


Fio spits out a lot of output. While running, fio will display the status of the jobs cre‐ ated. An example of that would be: Jobs: 1 (f=1): [_(1),M(1)][24.8%][r=20.5MiB/s,w=23.5MiB/s][r=82,w=94 IOPS][eta 01m: ↲ 31s] The characters inside the first set of square brackets denote the current status of each thread. The first character is the first job defined in the job file, and so forth. The possible values (in typical life cycle order) are: P Thread setup, but not started. C Thread created. I Thread initialized, waiting or generating necessary data. P Thread running pre-reading file(s). / Thread is in ramp period. R Running, doing sequential reads. r Running, doing random reads. W Running, doing sequential writes. w Running, doing random writes. M Running, doing mixed sequential reads/writes. m Running, doing mixed random reads/writes. D Running, doing sequential trims. d Running, doing random trims. F Running, currently waiting for fsync(2). V Running, doing verification of written data. f Thread finishing. E Thread exited, not reaped by main thread yet. - Thread reaped. X Thread reaped, exited with an error. K Thread reaped, exited due to signal. Fio will condense the thread string as not to take up more space on the command line than needed. For instance, if you have 10 readers and 10 writers running, the output would look like this: Jobs: 20 (f=20): [R(10),W(10)][4.0%][r=20.5MiB/s,w=23.5MiB/s][r=82,w=94 IOPS][eta 5 ↲ 7m:36s] Note that the status string is displayed in order, so it's possible to tell which of the jobs are currently doing what. In the example above this means that jobs 1--10 are readers and 11--20 are writers. The other values are fairly self explanatory -- number of threads currently running and doing I/O, the number of currently open files (f=), the estimated completion percentage, the rate of I/O since last check (read speed listed first, then write speed and optionally trim speed) in terms of bandwidth and IOPS, and time to completion for the current running group. It's impossible to estimate runtime of the following groups (if any). When fio is done (or interrupted by Ctrl-C), it will show the data for each thread, group of threads, and disks in that order. For each overall thread (or group) the output looks like: Client1: (groupid=0, jobs=1): err= 0: pid=16109: Sat Jun 24 12:07:54 2017 write: IOPS=88, BW=623KiB/s (638kB/s)(30.4MiB/50032msec) slat (nsec): min=500, max=145500, avg=8318.00, stdev=4781.50 clat (usec): min=170, max=78367, avg=4019.02, stdev=8293.31 lat (usec): min=174, max=78375, avg=4027.34, stdev=8291.79 clat percentiles (usec): | 1.00th=[ 302], 5.00th=[ 326], 10.00th=[ 343], 20.00th=[ 363], | 30.00th=[ 392], 40.00th=[ 404], 50.00th=[ 416], 60.00th=[ 445], | 70.00th=[ 816], 80.00th=[ 6718], 90.00th=[12911], 95.00th=[21627], | 99.00th=[43779], 99.50th=[51643], 99.90th=[68682], 99.95th=[72877], | 99.99th=[78119] bw ( KiB/s): min= 532, max= 686, per=0.10%, avg=622.87, stdev=24.82, samples= ↲ 100 iops : min= 76, max= 98, avg=88.98, stdev= 3.54, samples= 100 lat (usec) : 250=0.04%, 500=64.11%, 750=4.81%, 1000=2.79% lat (msec) : 2=4.16%, 4=1.84%, 10=4.90%, 20=11.33%, 50=5.37% lat (msec) : 100=0.65% cpu : usr=0.27%, sys=0.18%, ctx=12072, majf=0, minf=21 IO depths : 1=85.0%, 2=13.1%, 4=1.8%, 8=0.1%, 16=0.0%, 32=0.0%, >=64=0.0% submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% issued rwt: total=0,4450,0, short=0,0,0, dropped=0,0,0 latency : target=0, window=0, percentile=100.00%, depth=8 The job name (or first job's name when using group_reporting) is printed, along with the group id, count of jobs being aggregated, last error id seen (which is 0 when there are no errors), pid/tid of that thread and the time the job/group completed. Below are the I/O statistics for each data direction performed (showing writes in the example above). In the order listed, they denote: read/write/trim The string before the colon shows the I/O direction the statistics are for. IOPS is the average I/Os performed per second. BW is the average bandwidth rate shown as: value in power of 2 format (value in power of 10 format). The last two values show: (total I/O performed in power of 2 format / runtime of that thread). slat Submission latency (min being the minimum, max being the maximum, avg being the average, stdev being the standard deviation). This is the time it took to submit the I/O. For sync I/O this row is not displayed as the slat is really the completion latency (since queue/complete is one operation there). This value can be in nanoseconds, microseconds or milliseconds --- fio will choose the most appropriate base and print that (in the example above nanoseconds was the best scale). Note: in --minimal mode latencies are always expressed in microseconds. clat Completion latency. Same names as slat, this denotes the time from submis‐ sion to completion of the I/O pieces. For sync I/O, clat will usually be equal (or very close) to 0, as the time from submit to complete is basically just CPU time (I/O has already been done, see slat explanation). lat Total latency. Same names as slat and clat, this denotes the time from when fio created the I/O unit to completion of the I/O operation. bw Bandwidth statistics based on samples. Same names as the xlat stats, but also includes the number of samples taken (samples) and an approximate per‐ centage of total aggregate bandwidth this thread received in its group (per). This last value is only really useful if the threads in this group are on the same disk, since they are then competing for disk access. iops IOPS statistics based on samples. Same names as bw. lat (nsec/usec/msec) The distribution of I/O completion latencies. This is the time from when I/O leaves fio and when it gets completed. Unlike the separate read/write/trim sections above, the data here and in the remaining sections apply to all I/Os for the reporting group. 250=0.04% means that 0.04% of the I/Os com‐ pleted in under 250us. 500=64.11% means that 64.11% of the I/Os required 250 to 499us for completion. cpu CPU usage. User and system time, along with the number of context switches this thread went through, usage of system and user time, and finally the number of major and minor page faults. The CPU utilization numbers are aver‐ ages for the jobs in that reporting group, while the context and fault coun‐ ters are summed. IO depths The distribution of I/O depths over the job lifetime. The numbers are divided into powers of 2 and each entry covers depths from that value up to those that are lower than the next entry -- e.g., 16= covers depths from 16 to 31. Note that the range covered by a depth distribution entry can be dif‐ ferent to the range covered by the equivalent submit/complete distribution entry. IO submit How many pieces of I/O were submitting in a single submit call. Each entry denotes that amount and below, until the previous entry -- e.g., 16=100% means that we submitted anywhere between 9 to 16 I/Os per submit call. Note that the range covered by a submit distribution entry can be different to the range covered by the equivalent depth distribution entry. IO complete Like the above submit number, but for completions instead. IO issued rwt The number of read/write/trim requests issued, and how many of them were short or dropped. IO latency These values are for latency-target and related options. When these options are engaged, this section describes the I/O depth required to meet the spec‐ ified latency target. After each client has been listed, the group statistics are printed. They will look like this: Run status group 0 (all jobs): READ: bw=20.9MiB/s (21.9MB/s), 10.4MiB/s-10.8MiB/s (10.9MB/s-11.3MB/s), io=64.0M ↲ iB (67.1MB), run=2973-3069msec WRITE: bw=1231KiB/s (1261kB/s), 616KiB/s-621KiB/s (630kB/s-636kB/s), io=64.0MiB ( ↲ 67.1MB), run=52747-53223msec For each data direction it prints: bw Aggregate bandwidth of threads in this group followed by the minimum and maximum bandwidth of all the threads in this group. Values outside of brackets are power-of-2 format and those within are the equivalent value in a power-of-10 format. io Aggregate I/O performed of all threads in this group. The format is the same as bw. run The smallest and longest runtimes of the threads in this group. And finally, the disk statistics are printed. This is Linux specific. They will look like this: Disk stats (read/write): sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=10 ↲ 0.00% Each value is printed for both reads and writes, with reads first. The numbers denote: ios Number of I/Os performed by all groups. merge Number of merges performed by the I/O scheduler. ticks Number of ticks we kept the disk busy. in_queue Total time spent in the disk queue. util The disk utilization. A value of 100% means we kept the disk busy con‐ stantly, 50% would be a disk idling half of the time. It is also possible to get fio to dump the current output while it is running, without terminating the job. To do that, send fio the USR1 signal. You can also get regularly timed dumps by using the --status-interval parameter, or by creating a file in `/tmp' named `fio-dump-status'. If fio sees this file, it will unlink it and dump the current output status.


For scripted usage where you typically want to generate tables or graphs of the results, fio can output the results in a semicolon separated format. The format is one long line of values, such as: 2;card0;0;0;7139336;121836;60004;1;10109;27.932460;116.933948;220;126861;3495.44680 ↲ 7;1085.368601;226;126864;3523.635629;1089.012448;24063;99944;50.275485%;59818.274627;5540.657370;7155060;122104;60004;1;8338;29.086342;117.839068;388;128077;5032.488518;1234.785715;391;128085;5061.839412;1236.909129;23436;100928;50.287926%;59964.832030;5644.844189;14.595833%;19.394167%;123706;0;7313;0.1%;0.1%;0.1%;0.1%;0.1%;0.1%;100.0%;0.00%;0.00%;0.00%;0.00%;0.00%;0.00%;0.01%;0.02%;0.05%;0.16%;6.04%;40.40%;52.68%;0.64%;0.01%;0.00%;0.01%;0.00%;0.00%;0.00%;0.00%;0.00% A description of this job goes here. The job description (if provided) follows on a second line. To enable terse output, use the --minimal or `--output-format=terse' command line options. The first value is the version of the terse output format. If the output has to be changed for some reason, this number will be incremented by 1 to signify that change. Split up, the format is as follows (comments in brackets denote when a field was intro‐ duced or whether it's specific to some terse version): terse version, fio version [v3], jobname, groupid, error READ status: Total IO (KiB), bandwidth (KiB/sec), IOPS, runtime (msec) Submission latency: min, max, mean, stdev (usec) Completion latency: min, max, mean, stdev (usec) Completion latency percentiles: 20 fields (see below) Total latency: min, max, mean, stdev (usec) Bw (KiB/s): min, max, aggregate percentage of total, mean, stdev, number of sa ↲ mples [v5] IOPS [v5]: min, max, mean, stdev, number of samples WRITE status: Total IO (KiB), bandwidth (KiB/sec), IOPS, runtime (msec) Submission latency: min, max, mean, stdev (usec) Completion latency: min, max, mean, stdev (usec) Completion latency percentiles: 20 fields (see below) Total latency: min, max, mean, stdev (usec) Bw (KiB/s): min, max, aggregate percentage of total, mean, stdev, number of sa ↲ mples [v5] IOPS [v5]: min, max, mean, stdev, number of samples TRIM status [all but version 3]: Fields are similar to READ/WRITE status. CPU usage: user, system, context switches, major faults, minor faults I/O depths: <=1, 2, 4, 8, 16, 32, >=64 I/O latencies microseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000 I/O latencies milliseconds: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, 2000, >=2000 Disk utilization [v3]: disk name, read ios, write ios, read merges, write merges, read ticks, write t ↲ icks, time spent in queue, disk utilization percentage Additional Info (dependent on continue_on_error, default off): total # errors, first error code Additional Info (dependent on description being set): Text description Completion latency percentiles can be a grouping of up to 20 sets, so for the terse output fio writes all of them. Each field will look like this: 1.00%=6112 which is the Xth percentile, and the `usec' latency associated with it. For Disk utilization, all disks used by fio are shown. So for each disk there will be a disk utilization section. Below is a single line containing short names for each of the fields in the minimal output v3, separated by semicolons: terse_version_3;fio_version;jobname;groupid;error;read_kb;read_bandwidth;read_iops; ↲ read_runtime_ms;read_slat_min;read_slat_max;read_slat_mean;read_slat_dev;read_clat_min;read_clat_max;read_clat_mean;read_clat_dev;read_clat_pct01;read_clat_pct02;read_clat_pct03;read_clat_pct04;read_clat_pct05;read_clat_pct06;read_clat_pct07;read_clat_pct08;read_clat_pct09;read_clat_pct10;read_clat_pct11;read_clat_pct12;read_clat_pct13;read_clat_pct14;read_clat_pct15;read_clat_pct16;read_clat_pct17;read_clat_pct18;read_clat_pct19;read_clat_pct20;read_tlat_min;read_lat_max;read_lat_mean;read_lat_dev;read_bw_min;read_bw_max;read_bw_agg_pct;read_bw_mean;read_bw_dev;write_kb;write_bandwidth;write_iops;write_runtime_ms;write_slat_min;write_slat_max;write_slat_mean;write_slat_dev;write_clat_min;write_clat_max;write_clat_mean;write_clat_dev;write_clat_pct01;write_clat_pct02;write_clat_pct03;write_clat_pct04;write_clat_pct05;write_clat_pct06;write_clat_pct07;write_clat_pct08;write_clat_pct09;write_clat_pct10;write_clat_pct11;write_clat_pct12;write_clat_pct13;write_clat_pct14;write_clat_pct15;write_clat_pct16;write_clat_pct17;write_clat_pct18;write_clat_pct19;write_clat_pct20;write_tlat_min;write_lat_max;write_lat_mean;write_lat_dev;write_bw_min;write_bw_max;write_bw_agg_pct;write_bw_mean;write_bw_dev;cpu_user;cpu_sys;cpu_csw;cpu_mjf;cpu_minf;iodepth_1;iodepth_2;iodepth_4;iodepth_8;iodepth_16;iodepth_32;iodepth_64;lat_2us;lat_4us;lat_10us;lat_20us;lat_50us;lat_100us;lat_250us;lat_500us;lat_750us;lat_1000us;lat_2ms;lat_4ms;lat_10ms;lat_20ms;lat_50ms;lat_100ms;lat_250ms;lat_500ms;lat_750ms;lat_1000ms;lat_2000ms;lat_over_2000ms;disk_name;disk_read_iops;disk_write_iops;disk_read_merges;disk_write_merges;disk_read_ticks;write_ticks;disk_queue_time;disk_util


The json output format is intended to be both human readable and convenient for automated parsing. For the most part its sections mirror those of the normal output. The runtime value is reported in msec and the bw value is reported in 1024 bytes per second units. JSON+ OUTPUT The json+ output format is identical to the json output format except that it adds a full dump of the completion latency bins. Each bins object contains a set of (key, value) pairs where keys are latency durations and values count how many I/Os had completion latencies of the corresponding duration. For example, consider: "bins" : { "87552" : 1, "89600" : 1, "94720" : 1, "96768" : 1, "97792" : 1, "99840" : 1, "100864" : 2, "103936" : 6, "104960" : 534, "105984" : 5995, "107008" : 7529, ... } This data indicates that one I/O required 87,552ns to complete, two I/Os required 100,864ns to complete, and 7529 I/Os required 107,008ns to complete. Also included with fio is a Python script fio_jsonplus_clat2csv that takes json+ output and generates CSV-formatted latency data suitable for plotting. The latency durations actually represent the midpoints of latency intervals. For details refer to `stat.h' in the fio source.


There are two trace file format that you can encounter. The older (v1) format is unsup‐ ported since version 1.20-rc3 (March 2008). It will still be described below in case that you get an old trace and want to understand it. In any case the trace is a simple text file with a single action per line. Trace file format v1 Each line represents a single I/O action in the following format: rw, offset, length where `rw=0/1' for read/write, and the `offset' and `length' entries being in bytes. This format is not supported in fio versions >= 1.20-rc3. Trace file format v2 The second version of the trace file format was added in fio version 1.17. It allows to access more then one file per trace and has a bigger set of possible file actions. The first line of the trace file has to be: "fio version 2 iolog" Following this can be lines in two different formats, which are described below. The file management format: filename action The `filename' is given as an absolute path. The `action' can be one of these: add Add the given `filename' to the trace. open Open the file with the given `filename'. The `filename' has to have been added with the add action before. close Close the file with the given `filename'. The file has to have been opened before. The file I/O action format: filename action offset length The `filename' is given as an absolute path, and has to have been added and opened before it can be used with this format. The `offset' and `length' are given in bytes. The `action' can be one of these: wait Wait for `offset' microseconds. Everything below 100 is dis‐ carded. The time is relative to the previous `wait' state‐ ment. read Read `length' bytes beginning from `offset'. write Write `length' bytes beginning from `offset'. sync fsync(2) the file. datasync fdatasync(2) the file. trim Trim the given file from the given `offset' for `length' bytes.


In some cases, we want to understand CPU overhead in a test. For example, we test patches for the specific goodness of whether they reduce CPU usage. Fio implements a balloon approach to create a thread per CPU that runs at idle priority, meaning that it only runs when nobody else needs the cpu. By measuring the amount of work completed by the thread, idleness of each CPU can be derived accordingly. An unit work is defined as touching a full page of unsigned characters. Mean and standard deviation of time to complete an unit work is reported in "unit work" section. Options can be chosen to report detailed percpu idleness or overall system idleness by aggregating percpu stats.


Fio is usually run in one of two ways, when data verification is done. The first is a nor‐ mal write job of some sort with verify enabled. When the write phase has completed, fio switches to reads and verifies everything it wrote. The second model is running just the write phase, and then later on running the same job (but with reads instead of writes) to repeat the same I/O patterns and verify the contents. Both of these methods depend on the write phase being completed, as fio otherwise has no idea how much data was written. With verification triggers, fio supports dumping the current write state to local files. Then a subsequent read verify workload can load this state and know exactly where to stop. This is useful for testing cases where power is cut to a server in a managed fashion, for instance. A verification trigger consists of two things: 1) Storing the write state of each job. 2) Executing a trigger command. The write state is relatively small, on the order of hundreds of bytes to single kilo‐ bytes. It contains information on the number of completions done, the last X completions, etc. A trigger is invoked either through creation ('touch') of a specified file in the system, or through a timeout setting. If fio is run with `--trigger-file=/tmp/trigger-file', then it will continually check for the existence of `/tmp/trigger-file'. When it sees this file, it will fire off the trigger (thus saving state, and executing the trigger command). For client/server runs, there's both a local and remote trigger. If fio is running as a server backend, it will send the job states back to the client for safe storage, then exe‐ cute the remote trigger, if specified. If a local trigger is specified, the server will still send back the write state, but the client will then execute the trigger. Verification trigger example Let's say we want to run a powercut test on the remote Linux machine 'server'. Our write workload is in `write-test.fio'. We want to cut power to 'server' at some point during the run, and we'll run this test from the safety or our local machine, 'localbox'. On the server, we'll start the fio backend normally: server# fio --server and on the client, we'll fire off the workload: localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trig‐ ger-remote="bash -c "echo b > /proc/sysrq-triger"" We set `/tmp/my-trigger' as the trigger file, and we tell fio to execute: echo b > /proc/sysrq-trigger on the server once it has received the trigger and sent us the write state. This will work, but it's not really cutting power to the server, it's merely abruptly rebooting it. If we have a remote way of cutting power to the server through IPMI or similar, we could do that through a local trigger command instead. Let's assume we have a script that does IPMI reboot of a given hostname, ipmi-reboot. On local‐ box, we could then have run fio with a local trigger instead: localbox$ fio --client=server --trigger-file=/tmp/my-trigger --trig‐ ger="ipmi-reboot server" For this case, fio would wait for the server to send us the write state, then exe‐ cute `ipmi-reboot server' when that happened. Loading verify state To load stored write state, a read verification job file must contain the ver‐ ify_state_load option. If that is set, fio will load the previously stored state. For a local fio run this is done by loading the files directly, and on a client/server run, the server backend will ask the client to send the files over and load them from there.


Fio supports a variety of log file formats, for logging latencies, bandwidth, and IOPS. The logs share a common format, which looks like this: time (msec), value, data direction, block size (bytes), offset (bytes) `Time' for the log entry is always in milliseconds. The `value' logged depends on the type of log, it will be one of the following: Latency log Value is latency in nsecs Bandwidth log Value is in KiB/sec IOPS log Value is IOPS `Data direction' is one of the following: 0 I/O is a READ 1 I/O is a WRITE 2 I/O is a TRIM The entry's `block size' is always in bytes. The `offset' is the offset, in bytes, from the start of the file, for that particular I/O. The logging of the offset can be toggled with log_offset. Fio defaults to logging every individual I/O. When IOPS are logged for individual I/Os the `value' entry will always be 1. If windowed logging is enabled through log_avg_msec, fio logs the average values over the specified period of time. If windowed logging is enabled and log_max_value is set, then fio logs maximum values in that window instead of averages. Since `data direction', `block size' and `offset' are per-I/O values, if windowed logging is enabled they aren't applicable and will be 0. CLIENT / SERVER Normally fio is invoked as a stand-alone application on the machine where the I/O workload should be generated. However, the backend and frontend of fio can be run separately i.e., the fio server can generate an I/O workload on the "Device Under Test" while being con‐ trolled by a client on another machine. Start the server on the machine which has access to the storage DUT: $ fio --server=args where `args' defines what fio listens to. The arguments are of the form `type,hostname' or `IP,port'. `type' is either `ip' (or ip4) for TCP/IP v4, `ip6' for TCP/IP v6, or `sock' for a local unix domain socket. `hostname' is either a hostname or IP address, and `port' is the port to listen to (only valid for TCP/IP, not a local socket). Some examples: 1) fio --server Start a fio server, listening on all interfaces on the default port (8765). 2) fio --server=ip:hostname,4444 Start a fio server, listening on IP belonging to hostname and on port 4444. 3) fio --server=ip6:::1,4444 Start a fio server, listening on IPv6 localhost ::1 and on port 4444. 4) fio --server=,4444 Start a fio server, listening on all interfaces on port 4444. 5) fio --server= Start a fio server, listening on IP on the default port. 6) fio --server=sock:/tmp/fio.sock Start a fio server, listening on the local socket `/tmp/fio.sock'. Once a server is running, a "client" can connect to the fio server with: $ fio <local-args> --client=<server> <remote-args> <job file(s)> where `local-args' are arguments for the client where it is running, `server' is the con‐ nect string, and `remote-args' and `job file(s)' are sent to the server. The `server' string follows the same format as it does on the server side, to allow IP/hostname/socket and port strings. Fio can connect to multiple servers this way: $ fio --client=<server1> <job file(s)> --client=<server2> <job file(s)> If the job file is located on the fio server, then you can tell the server to load a local file as well. This is done by using --remote-config: $ fio --client=server --remote-config /path/to/file.fio Then fio will open this local (to the server) job file instead of being passed one from the client. If you have many servers (example: 100 VMs/containers), you can input a pathname of a file containing host IPs/names as the parameter value for the --client option. For example, here is an example `host.list' file containing 2 hostnames: host1.your.dns.domain host2.your.dns.domain The fio command would then be: $ fio --client=host.list <job file(s)> In this mode, you cannot input server-specific parameters or job files -- all servers receive the same job file. In order to let `fio --client' runs use a shared filesystem from multiple hosts, `fio --client' now prepends the IP address of the server to the filename. For example, if fio is using the directory `/mnt/nfs/fio' and is writing filename `fileio.tmp', with a --client `hostfile' containing two hostnames `h1' and `h2' with IP addresses and, then fio will create two files: /mnt/nfs/fio/ /mnt/nfs/fio/


fio was written by Jens Axboe <>, now Jens Axboe <>. This man page was written by Aaron Carroll <> based on documentation by Jens Axboe. This man page was rewritten by Tomohiro Kusumi <> based on documentation by Jens Axboe.


Report bugs to the fio mailing list <>. See REPORTING-BUGS. REPORTING-BUGS:


For further documentation see HOWTO and README. Sample jobfiles are available in the `examples/' directory. These are typically located under `/usr/share/doc/fio'. HOWTO: README:
User Manual August 2017 fio(1)
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fio(1) referred by ioping(1) | iowatcher(1)
refer to aio_read(3) | aio_write(3) | blktrace(8) | clock_getres(2) | elvi(1sr) | fallocate(2) | fcntl(2) | fsync(2) | gettimeofday(2) | ionice(1) | lseek(2) | malloc(3) | mlock(2) | mmap(2) | nice(2) | posix_fadvise(2) | posix_fallocate(3) | pread(2) | pthread_create(3) | read(2)
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