Units

kb_base=int

Select the interpretation of unit prefixes in input parameters.

unit_base=int

Base unit for reporting. Allowed values are:

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 workload 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

Limit runtime. The test will run until it completes the configured I/O workload or until it has run for this specified amount of time, whichever occurs first. 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 interpreted 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:

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 gettimeofday(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.

job_start_clock_id=int

The clock_id passed to the call to clock_gettime used to record job_start in the json output format. Default is 0, or CLOCK_REALTIME.

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 filename(s) are set fio will use the first listed directory, and thereby matching the filename semantic (which generates a file for each clone if not specified, but lets all clones use the same file if set).

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 override 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 `filename=/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.

filename_format=str

If sharing multiple files between jobs, it is usually necessary to have fio generate 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 keywords in this string:

unique_filename=bool

To avoid collisions between networked clients, fio defaults to prefixing any generated filenames (with a directory specified) with the source of the client connecting. To disable this behavior, set this option to 0.

opendir=str

Recursively open any files below directory str. This accepts only a single directory and unlike related options, colons appearing in the path must not be escaped.

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:

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:

ioscheduler=str

Attempt to switch the device hosting the file to the specified I/O scheduler before running. If the file is a pipe, a character device file or if device hosting the file could not be determined, this option is ignored.

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 executed. 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 (delete) 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 (delete) job files after each iteration or loop. Default: false.

zonemode=str

Accepted values are:

zonerange=int

For zonemode=strided, this is the size of a single zone. See also zonesize and zoneskip.

For zonemode=zbd, this parameter is ignored.

zonesize=int

For zonemode=strided, this is the number of bytes to transfer before skipping zoneskip bytes. If this parameter is smaller than zonerange then only a fraction of each zone with zonerange bytes will be accessed. If this parameter is larger than zonerange then each zone will be accessed multiple times before skipping to the next zone.

For zonemode=zbd, this is the size of a single zone. The zonerange parameter is ignored in this mode. For a job accessing a zoned block device, the specified zonesize must be 0 or equal to the device zone size. For a regular block device or file, the specified zonesize must be at least 512B.

zonecapacity=int

For zonemode=zbd, this defines the capacity of a single zone, which is the accessible area starting from the zone start address. This parameter only applies when using zonemode=zbd in combination with regular block devices. If not specified it defaults to the zone size. If the target device is a zoned block device, the zone capacity is obtained from the device information and this option is ignored.

zoneskip=int[z]

For zonemode=strided, the number of bytes to skip after zonesize bytes of data have been transferred.

For zonemode=zbd, the zonesize aligned number of bytes to skip once a zone is fully written (write workloads) or all written data in the zone have been read (read workloads). This parameter is valid only for sequential workloads and ignored for random workloads. For read workloads, see also read_beyond_wp.

read_beyond_wp=bool

This parameter applies to zonemode=zbd only.

Zoned block devices are block devices that consist of multiple zones. Each zone has a type, e.g. conventional or sequential. A conventional zone can be written at any offset that is a multiple of the block size. Sequential zones must be written sequentially. The position at which a write must occur is called the write pointer. A zoned block device can be either host managed or host aware. For host managed devices the host must ensure that writes happen sequentially. Fio recognizes host managed devices and serializes writes to sequential zones for these devices.

If a read occurs in a sequential zone beyond the write pointer then the zoned block device will complete the read without reading any data from the storage medium. Since such reads lead to unrealistically high bandwidth and IOPS numbers fio only reads beyond the write pointer if explicitly told to do so. Default: false.

max_open_zones=int

When a zone of a zoned block device is partially written (i.e. not all sectors of the zone have been written), the zone is in one of three conditions: 'implicit open', 'explicit open' or 'closed'. Zoned block devices may have a limit called 'max_open_zones' (same name as the parameter) on the total number of zones that can simultaneously be in the 'implicit open' or 'explicit open' conditions. Zoned block devices may have another limit called 'max_active_zones', on the total number of zones that can simultaneously be in the three conditions. The max_open_zones parameter limits the number of zones to which write commands are issued by all fio jobs, that is, limits the number of zones that will be in the conditions. When the device has the max_open_zones limit and does not have the max_active_zones limit, the max_open_zones parameter limits the number of zones in the two open conditions up to the limit. In this case, fio includes zones in the two open conditions to the write target zones at fio start. When the device has both the max_open_zones and the max_active_zones limits, the max_open_zones parameter limits the number of zones in the three conditions up to the limit. In this case, fio includes zones in the three conditions to the write target zones at fio start.

This parameter is relevant only if the zonemode=zbd is used. The default value is always equal to the max_open_zones limit of the target zoned block device and a value higher than this limit cannot be specified by users unless the option ignore_zone_limits is specified. When ignore_zone_limits is specified or the target device does not have the max_open_zones limit, max_open_zones can specify 0 to disable any limit on the number of zones that can be simultaneously written to by all jobs.

job_max_open_zones=int

In the same manner as max_open_zones, limit the number of open zones per fio job, that is, the number of zones that a single job can simultaneously write to. A value of zero indicates no limit. Default: zero.

ignore_zone_limits=bool

If this option is used, fio will ignore the maximum number of open zones limit of the zoned block device in use, thus allowing the option max_open_zones value to be larger than the device reported limit. Default: false.

zone_reset_threshold=float

A number between zero and one that indicates the ratio of written bytes in the zones with write pointers in the IO range to the size of the IO range. When current ratio is above this ratio, zones are reset periodically as zone_reset_frequency specifies. If there are multiple jobs when using this option, the IO range for all write jobs has to be the same.

zone_reset_frequency=float

A number between zero and one that indicates how often a zone reset should be issued if the zone reset threshold has been exceeded. A zone reset is submitted after each (1 / zone_reset_frequency) write requests. This and the previous parameter can be used to simulate garbage collection activity.

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.

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:

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:

unified_rw_reporting=str

Fio normally reports statistics on a per data direction basis, meaning that reads, writes, and trims are accounted and reported separately. This option determines whether fio reports the results normally, summed together, or as both options. Accepted values are:

randrepeat=bool

Seed all random number generators in a predictable way so the pattern is repeatable across runs. Default: true.

allrandrepeat=bool

Alias for randrepeat. Default: true.

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:

fadvise_hint=str

Use posix_fadvise(2) or posix_madvise(2) to advise the kernel what I/O patterns are likely to be issued. Accepted values are:

write_hint=str

Use fcntl(2) to advise the kernel what life time to expect from a write. Only supported on Linux, as of version 4.13. Accepted values are:

offset=int[%|z]

Start I/O at the provided offset in the file, given as either a fixed size in bytes, zones or a percentage. If a percentage is given, the generated offset will be aligned to the minimum blocksize or to the value of offset_align if provided. 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%. In ZBD mode, value can be set as number of zones using 'z'.

offset_align=int

If set to non-zero value, the byte offset generated by a percentage offset is aligned upwards to this value. Defaults to 0 meaning that a percentage offset is aligned to the minimum block size.

offset_increment=int[%|z]

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 incremented 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 parallel disjoint segments, with even spacing between the starting points. Percentages can be used for this option. If a percentage is given, the generated offset will be aligned to the minimum blocksize or to the value of offset_align if provided.In ZBD mode, value can be set as number of zones using 'z'.

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 Windows, DragonFlyBSD or OSX 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:

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[: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:

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 percentages. 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., partially-overwritten blocks are ignored. With an async I/O engine and an I/O depth > 1, it is possible for the same block to be overwritten, which can cause verification errors. Either do not use norandommap in this case, or also use the lfsr random generator.

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 disabled by default.

random_generator=str

Fio supports the following engines for generating I/O offsets for random I/O:

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:

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:

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:

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 blocksize 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 followed by fixed pattern data. The fixed pattern is either zeros, or the pattern specified by buffer_pattern. If the buffer_pattern option is used, it might skew the compression ratio slightly. Setting buffer_compress_percentage to a value other than 100 will also enable refill_buffers in order to reduce the likelihood that adjacent blocks are so similar that they over compress when seen together. See buffer_compress_chunk for how to set a finer or coarser granularity of the random/fixed data regions. Defaults to unset i.e., buffer data will not adhere to any compression level.

buffer_compress_chunk=int

This setting allows fio to manage how big the random/fixed data region is when using buffer_compress_percentage. When buffer_compress_chunk is set to some non-zero value smaller than the block size, fio can repeat the random/fixed region throughout the I/O buffer at the specified interval (which particularly useful when bigger block sizes are used for a job). When set to 0, fio will use a chunk size that matches the block size resulting in a single random/fixed region within the I/O buffer. Defaults to 512. When the unit is omitted, the value is interpreted in bytes.

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:

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 individual buffers either fully compressible, or not at all -- this option only controls the distribution of unique buffers. Setting this option will also enable refill_buffers to prevent every buffer being identical.

dedupe_mode=str

If dedupe_percentage is given, then this option controls how fio generates the dedupe buffers.

dedupe_working_set_percentage=int

If dedupe_mode is set to working_set, then this controls the percentage of size of the file or device used as the buffers fio will choose to generate the dedupe buffers from

dedupe_global=bool

This controls whether the deduplication buffers will be shared amongst all jobs that have this option set. The buffers are spread evenly between participating jobs.

I/O size

size=int[%|z]

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 altered by other means such as (1) runtime, (2) io_size, (3) number_ios, (4) gaps/holes while doing I/O's such as `rw=read:16K', or (5) sequential I/O reaching end of the file which is possible when percentage_random is less than 100. 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. In ZBD mode, size can be given in units of number of zones using 'z'. Can be combined with offset to constrain the start and end range that I/O will be done within.

io_size=int[%|z], io_limit=int[%|z]

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. Value can be set as percentage: io_size=N%. In this case io_size multiplies size= value. In ZBD mode, value can also be set as number of zones using 'z'.

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. If not given, each created file is the same size. This option overrides size in terms of file size, i.e. size becomes merely the default for io_size (and has no effect it all if io_size is set explicitly).

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) or EDQUOT (disk quota exceeded) 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.

I/O engine

ioengine=str

fio supports 2 kinds of performance measurement: I/O and file/directory operation.

I/O engines define how the job issues I/O to the file. The following types are defined:

File/directory operation engines define how the job operates file or directory. The following types are defined:

For file and directory operation engines, there is no I/O throughput, then the statistics data in report have different meanings. The meaningful output indexes are: iops and clat. bw is meaningless. Refer to section: "Interpreting the output" for more details.

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.

(io_uring,libaio)cmdprio_percentage=int[,int]

Set the percentage of I/O that will be issued with the highest priority. Default: 0. A single value applies to reads and writes. Comma-separated values may be specified for reads and writes. For this option to be effective, NCQ priority must be supported and enabled, and `direct=1' option must be used. fio must also be run as the root user. Unlike slat/clat/lat stats, which can be tracked and reported independently, per priority stats only track and report a single type of latency. By default, completion latency (clat) will be reported, if lat_percentiles is set, total latency (lat) will be reported.

(io_uring,libaio)cmdprio_class=int[,int]

Set the I/O priority class to use for I/Os that must be issued with a priority when cmdprio_percentage or cmdprio_bssplit is set. If not specified when cmdprio_percentage or cmdprio_bssplit is set, this defaults to the highest priority class. A single value applies to reads and writes. Comma-separated values may be specified for reads and writes. See man ionice(1). See also the prioclass option.

(io_uring,libaio)cmdprio_hint=int[,int]

Set the I/O priority hint to use for I/Os that must be issued with a priority when cmdprio_percentage or cmdprio_bssplit is set. If not specified when cmdprio_percentage or cmdprio_bssplit is set, this defaults to 0 (no hint). A single value applies to reads and writes. Comma-separated values may be specified for reads and writes. See also the priohint option.

(io_uring,libaio)cmdprio=int[,int]

Set the I/O priority value to use for I/Os that must be issued with a priority when cmdprio_percentage or cmdprio_bssplit is set. If not specified when cmdprio_percentage or cmdprio_bssplit is set, this defaults to 0. Linux limits us to a positive value between 0 and 7, with 0 being the highest. A single value applies to reads and writes. Comma-separated values may be specified for reads and writes. See man ionice(1). Refer to an appropriate manpage for other operating systems since the meaning of priority may differ. See also the prio option.

(io_uring,libaio)cmdprio_bssplit=str[,str]

To get a finer control over I/O priority, this option allows specifying the percentage of IOs that must have a priority set depending on the block size of the IO. This option is useful only when used together with the option bssplit, that is, multiple different block sizes are used for reads and writes.

(io_uring,io_uring_cmd)fixedbufs

If fio is asked to do direct IO, then Linux will map pages for each IO call, and release them when IO is done. If this option is set, the pages are pre-mapped before IO is started. This eliminates the need to map and release for each IO. This is more efficient, and reduces the IO latency as well.

(io_uring,io_uring_cmd)nonvectored=int

With this option, fio will use non-vectored read/write commands, where address must contain the address directly. Default is -1.

(io_uring,io_uring_cmd)force_async

Normal operation for io_uring is to try and issue an sqe as non-blocking first, and if that fails, execute it in an async manner. With this option set to N, then every N request fio will ask sqe to be issued in an async manner. Default is 0.

(io_uring,io_uring_cmd,xnvme)hipri

If this option is set, fio will attempt to use polled IO completions. Normal IO completions generate interrupts to signal the completion of IO, polled completions do not. Hence they are require active reaping by the application. The benefits are more efficient IO for high IOPS scenarios, and lower latencies for low queue depth IO.

(io_uring,io_uring_cmd)registerfiles

With this option, fio registers the set of files being used with the kernel. This avoids the overhead of managing file counts in the kernel, making the submission and completion part more lightweight. Required for the below sqthread_poll option.

(io_uring,io_uring_cmd,xnvme)sqthread_poll

Normally fio will submit IO by issuing a system call to notify the kernel of available items in the SQ ring. If this option is set, the act of submitting IO will be done by a polling thread in the kernel. This frees up cycles for fio, at the cost of using more CPU in the system. As submission is just the time it takes to fill in the sqe entries and any syscall required to wake up the idle kernel thread, fio will not report submission latencies.

(io_uring,io_uring_cmd)sqthread_poll_cpu=int

When `sqthread_poll` is set, this option provides a way to define which CPU should be used for the polling thread.

(io_uring_cmd)cmd_type=str

Specifies the type of uring passthrough command to be used. Supported value is nvme. Default is nvme.

(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 priority. The default is 100%.

(pvsync2,libaio,io_uring,io_uring_cmd)nowait=bool

By default if a request cannot be executed immediately (e.g. resource starvation, waiting on locks) it is queued and the initiating process will be blocked until the required resource becomes free. This option sets the RWF_NOWAIT flag (supported from the 4.14 Linux kernel) and the call will return instantly with EAGAIN or a partial result rather than waiting.

It is useful to also use ignore_error=EAGAIN when using this option. Note: glibc 2.27, 2.28 have a bug in syscall wrappers preadv2, pwritev2. They return EOPNOTSUP instead of EAGAIN.

For cached I/O, using this option usually means a request operates only with cached data. Currently the RWF_NOWAIT flag does not supported for cached write. For direct I/O, requests will only succeed if cache invalidation isn't required, file blocks are fully allocated and the disk request could be issued immediately.

(pvsync2,libaio,io_uring)atomic=bool

This option means that writes are issued with torn-write protection, meaning that for a power fail or kernel crash, all or none of the data from the write will be stored, but never a mix of old and new data. Torn-write protection is also known as atomic writes.

This option sets the RWF_ATOMIC flag (supported from the 6.11 Linux kernel) on a per-IO basis.

Writes with RWF_ATOMIC set will be rejected by the kernel when the file does not support torn-write protection. To learn a file's torn-write limits, issue statx with STATX_WRITE_ATOMIC.

(io_uring_cmd,xnvme)fdp=bool

Enable Flexible Data Placement mode for write commands.

(io_uring_cmd,xnvme)dataplacement=str

Specifies the data placement directive type to use for write commands. The following types are supported:

(io_uring_cmd,xnvme)plid_select=str,fdp_pli_select=str

Defines how fio decides which placement ID to use next. The following types are defined:

(io_uring_cmd,xnvme)plids=str,fdp_pli=str

Select which Placement ID Indices (FDP) or Placement IDs (streams) this job is allowed to use for writes. This option accepts a comma-separated list of values or ranges (e.g., 1,2-4,5,6-8).

For FDP by default, the job will cycle through all available Placement IDs, so use this option to be selective. The values specified here are array indices for the list of placement IDs returned by the nvme-cli command `nvme fdp status'. If you want fio to use FDP placement identifiers only at indices 0, 2 and 5, set `plids=0,2,5'.

For streams this should be a list of Stream IDs.

(io_uring_cmd,xnvme)dp_scheme=str

Defines which placement ID (index) to be selected based on offset(LBA) range. The file should contains one or more scheme entries in the following format:

(io_uring_cmd,xnvme)md_per_io_size=int

Size in bytes for separate metadata buffer per IO. Default: 0.

(io_uring_cmd,xnvme)pi_act=int

Action to take when nvme namespace is formatted with protection information. If this is set to 1 and namespace is formatted with metadata size equal to protection information size, fio won't use separate metadata buffer or extended logical block. If this is set to 1 and namespace is formatted with metadata size greater than protection information size, fio will not generate or verify the protection information portion of metadata for write or read case respectively. If this is set to 0, fio generates protection information for write case and verifies for read case. Default: 1.

For 16 bit CRC generation fio will use isa-l if available otherwise it will use the default slower generator. (see: https://github.com/intel/isa-l)

(io_uring_cmd,xnvme)pi_chk=str[,str][,str]

Controls the protection information check. This can take one or more of these values. Default: none.

(io_uring_cmd,xnvme)apptag=int

Specifies logical block application tag value, if namespace is formatted to use end to end protection information. Default: 0x1234.

(io_uring_cmd,xnvme)apptag_mask=int

Specifies logical block application tag mask value, if namespace is formatted to use end to end protection information. Default: 0xffff.

(io_uring_cmd)num_range=int

For trim command this will be the number of ranges to trim per I/O request. The number of logical blocks per range is determined by the bs option which should be a multiple of logical block size. This cannot be used with read or write. Note that setting this option > 1, log_offset will not be able to log all the offsets. Default: 1.

(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)cpumode=str

Specify how to stress the CPU. It can take these two values:

(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=int

The listening port of the HFDS cluster namenode.

(netsplice,net)port=int

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.

(rdma)port=int

The port to use for RDMA-CM communication. This should be the same value on the client and the server side.

(netsplice,net,rdma)hostname=str

The hostname or IP address to use for TCP, UDP or RDMA-CM 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:

(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 measures how long it took for the other end to receive and send back. For UDP multicast 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:

(rbd,rados)clustername=str

Specifies the name of the Ceph cluster.

(rbd)rbdname=str

Specifies the name of the RBD.

(rbd,rados)pool=str

Specifies the name of the Ceph pool containing RBD or RADOS data.

(rbd,rados)clientname=str

Specifies the username (without the 'client.' prefix) used to access the Ceph cluster. If the clustername is specified, the clientname shall be the full *type.id* string. If no type. prefix is given, fio will add 'client.' by default.

(rados)conf=str

Specifies the configuration path of ceph cluster, so conf file does not have to be /etc/ceph/ceph.conf.

(rbd,rados)busy_poll=bool

Poll store instead of waiting for completion. Usually this provides better throughput at cost of higher(up to 100%) CPU utilization.

(rados)touch_objects=bool

During initialization, touch (create if do not exist) all objects (files). Touching all objects affects ceph caches and likely impacts test results. Enabled by default.

(http)http_host=str

Hostname to connect to. HTTP port 80 is used automatically when the value of the https parameter is off, and HTTPS port 443 if it is A virtual-hosted-style S3 hostname starts with a bucket name, while a path-style S3 hostname does not. Default is localhost.

(http)http_user=str

Username for HTTP authentication.

(http)http_pass=str

Password for HTTP authentication.

(http)https=str

Whether to use HTTPS instead of plain HTTP. on enables HTTPS; insecure will enable HTTPS, but disable SSL peer verification (use with caution!). Default is off.

(http)http_mode=str

Which HTTP access mode to use: webdav, swift, or s3. Default is webdav.

(http)http_s3_region=str

The S3 region/zone to include in the request. Default is us-east-1.

(http)http_s3_key=str

The S3 secret key.

(http)http_s3_keyid=str

The S3 key/access id.

(http)http_s3_sse_customer_key=str

The encryption customer key in SSE server side.

(http)http_s3_sse_customer_algorithm=str

The encryption customer algorithm in SSE server side. Default is AES256

(http)http_s3_storage_class=str

Which storage class to access. User-customizable settings. Default is STANDARD

(http)http_swift_auth_token=str

The Swift auth token. See the example configuration file on how to retrieve this.

(http)http_verbose=int

Enable verbose requests from libcurl. Useful for debugging. 1 turns on verbose logging from libcurl, 2 additionally enables HTTP IO tracing. Default is 0

(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.

(rdma)verb=str

The RDMA verb to use on this side of the RDMA ioengine connection. Valid values are write, read, send and recv. These correspond to the equivalent RDMA verbs (e.g. write = rdma_write etc.). Note that this only needs to be specified on the client side of the connection. See the examples folder.

(rdma)bindname=str

The name to use to bind the local RDMA-CM connection to a local RDMA device. This could be a hostname or an IPv4 or IPv6 address. On the server side this will be passed into the rdma_bind_addr() function and on the client site it will be used in the rdma_resolve_add() function. This can be useful when multiple paths exist between the client and the server or in certain loopback configurations.

(filestat)stat_type=str

Specify stat system call type to measure lookup/getattr performance. Default is stat for stat(2).

(sg)hipri

If this option is set, fio will attempt to use polled IO completions. This will have a similar effect as (io_uring)hipri. Only SCSI READ and WRITE commands will have the SGV4_FLAG_HIPRI set (not UNMAP (trim) nor VERIFY). Older versions of the Linux sg driver that do not support hipri will simply ignore this flag and do normal IO. The Linux SCSI Low Level Driver (LLD) that "owns" the device also needs to support hipri (also known as iopoll and mq_poll). The MegaRAID driver is an example of a SCSI LLD. Default: clear (0) which does normal (interrupted based) IO.

(sg,io_uring_cmd)readfua=bool

With readfua option set to 1, read operations include the force unit access (fua) flag. Default: 0.

(sg,io_uring_cmd)writefua=bool

With writefua option set to 1, write operations include the force unit access (fua) flag. Default: 0.

(io_uring_cmd)write_mode=str

Specifies the type of write operation. Defaults to 'write'.

(io_uring_cmd)verify_mode=str

Specifies the type of command to be used in the verification phase. Defaults to 'read'.

(sg)sg_write_mode=str

Specify the type of write commands to issue. This option can take multiple values:

(sg)stream_id=int

Set the stream identifier for WRITE STREAM commands. If this is set to 0 (which is not a valid stream identifier) fio will open a stream and then close it when done. Default is 0.

(nbd)uri=str

Specify the NBD URI of the server to test. The string is a standard NBD URI (see https://github.com/NetworkBlockDevice/nbd/tree/master/doc). Example URIs:

(libcufile)gpu_dev_ids=str

Specify the GPU IDs to use with CUDA. This is a colon-separated list of int. GPUs are assigned to workers roundrobin. Default is 0.

(libcufile)cuda_io=str

Specify the type of I/O to use with CUDA. This option takes the following values:

(dfs)pool

Specify the label or UUID of the DAOS pool to connect to.

(dfs)cont

Specify the label or UUID of the DAOS container to open.

(dfs)chunk_size

Specify a different chunk size (in bytes) for the dfs file. Use DAOS container's chunk size by default.

(dfs)object_class

Specify a different object class for the dfs file. Use DAOS container's object class by default.

(nfs)nfs_url

URL in libnfs format, eg nfs://<server|ipv4|ipv6>/path[?arg=val[&arg=val]*] Refer to the libnfs README for more details.

(exec)program=str

Specify the program to execute. Note the program will receive a SIGTERM when the job is reaching the time limit. A SIGKILL is sent once the job is over. The delay between the two signals is defined by grace_time option.

(exec)arguments=str

Specify arguments to pass to program. Some special variables can be expanded to pass fio's job details to the program :

(exec)grace_time=int

Defines the time between the SIGTERM and SIGKILL signals. Default is 1 second.

(exec)std_redirect=bool

If set, stdout and stderr streams are redirected to files named from the job name. Default is true.

(xnvme)xnvme_async=str

Select the xnvme async command interface. This can take these values.

(xnvme)xnvme_sync=str

Select the xnvme synchronous command interface. This can take these values.

(xnvme)xnvme_admin=str

Select the xnvme admin command interface. This can take these values.

(xnvme)xnvme_dev_nsid=int

xnvme namespace identifier for userspace NVMe driver SPDK or vfio.

(xnvme)xnvme_dev_subnqn=str

Sets the subsystem NQN for fabrics. This is for xNVMe to utilize a fabrics target with multiple systems.

(xnvme)xnvme_mem=str

Select the xnvme memory backend. This can take these values.

(xnvme)xnvme_iovec

If this option is set, xnvme will use vectored read/write commands.

(libblkio)libblkio_driver=str

The libblkio driver to use. Different drivers access devices through different underlying interfaces. Available drivers depend on the libblkio version in use and are listed at https://libblkio.gitlab.io/libblkio/blkio.html#drivers

(libblkio)libblkio_path=str

Sets the value of the driver-specific "path" property before connecting the libblkio instance, which identifies the target device or file on which to perform I/O. Its exact semantics are driver-dependent and not all drivers may support it; see https://libblkio.gitlab.io/libblkio/blkio.html#drivers

(libblkio)libblkio_pre_connect_props=str

A colon-separated list of additional libblkio properties to be set after creating but before connecting the libblkio instance. Each property must have the format <name>=<value>. Colons can be escaped as \:. These are set after the engine sets any other properties, so those can be overridden. Available properties depend on the libblkio version in use and are listed at https://libblkio.gitlab.io/libblkio/blkio.html#properties

(libblkio)libblkio_num_entries=int

Sets the value of the driver-specific "num-entries" property before starting the libblkio instance. Its exact semantics are driver-dependent and not all drivers may support it; see https://libblkio.gitlab.io/libblkio/blkio.html#drivers

(libblkio)libblkio_queue_size=int

Sets the value of the driver-specific "queue-size" property before starting the libblkio instance. Its exact semantics are driver-dependent and not all drivers may support it; see https://libblkio.gitlab.io/libblkio/blkio.html#drivers

(libblkio)libblkio_pre_start_props=str

A colon-separated list of additional libblkio properties to be set after connecting but before starting the libblkio instance. Each property must have the format <name>=<value>. Colons can be escaped as \:. These are set after the engine sets any other properties, so those can be overridden. Available properties depend on the libblkio version in use and are listed at https://libblkio.gitlab.io/libblkio/blkio.html#properties

(libblkio)hipri

Use poll queues. This is incompatible with libblkio_wait_mode=eventfd and libblkio_force_enable_completion_eventfd.

(libblkio)libblkio_vectored

Submit vectored read and write requests.

(libblkio)libblkio_write_zeroes_on_trim

Submit trims as "write zeroes" requests instead of discard requests.

(libblkio)libblkio_wait_mode=str

How to wait for completions:

(libblkio)libblkio_force_enable_completion_eventfd

Enable the queue's completion eventfd even when unused. This may impact performance. The default is to enable it only if libblkio_wait_mode=eventfd.

(windowsaio)no_completion_thread

Avoid using a separate thread for completion polling.

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 kernel. 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 system 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_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 indeterminate/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 overlapping region has a non-zero size. Setting serialize_overlap tells fio to avoid provoking 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.

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). Note that this option cannot reliably be used with async IO engines.

I/O rate

thinkcycles=int

Stall the job for the specified number of cycles after an I/O has completed before issuing the next. May be used to simulate processing being done by an application. This is not taken into account for the time to be waited on for thinktime. Might not have any effect on some platforms, this can be checked by trying a setting a high enough amount of thinkcycles.

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 thinktime_blocks, thinktime_iotime 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 thinktime. In other words, this setting effectively caps the queue depth if the latter is larger.

thinktime_blocks_type=str

Only valid if thinktime is set - control how thinktime_blocks triggers. The default is `complete', which triggers thinktime when fio completes thinktime_blocks blocks. If this is set to `issue', then the trigger happens at the issue side.

thinktime_iotime=time

Only valid if thinktime is set - control thinktime interval by time. The thinktime stall is repeated after IOs are executed for thinktime_iotime. For example, `--thinktime_iotime=9s --thinktime=1s' repeat 10-second cycle with IOs for 9 seconds and stall for 1 second. When the unit is omitted, thinktime_iotime is interpreted as a number of seconds. If this option is used together with thinktime_blocks, the thinktime stall is repeated after thinktime_iotime or after thinktime_blocks IOs, whichever happens first.

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.

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 specified 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 specified 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 values 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-separated values may be specified for reads, writes, and trims as described in blocksize.

rate_process=str

This option controls how fio manages rated I/O submissions. The default is `linear', 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 (https://en.wikipedia.org/wiki/Poisson_point_process). The lambda will be 10^6 / IOPS for the given workload.

rate_ignore_thinktime=bool

By default, fio will attempt to catch up to the specified rate setting, if any kind of thinktime setting was used. If this option is set, then fio will ignore the thinktime and continue doing IO at the specified rate, instead of entering a catch-up mode after thinktime is done.

rate_cycle=int

Average bandwidth for rate_min and rate_iops_min over this number of milliseconds. Defaults to 1000.

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 omitted, the value is interpreted in microseconds. See latency_window and latency_percentile.

latency_window=time

Used with latency_target to specify the sample window that the job is run at varying 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_target 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.

latency_run=bool

Used with latency_target. If false (default), fio will find the highest queue depth that meets latency_target and exit. If true, fio will continue running and try to meet latency_target by adjusting queue depth.

max_latency=time[,time][,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. Comma-separated values may be specified for reads, writes, and trims as described in blocksize.

I/O replay

write_iolog=str

Write the issued I/O patterns to the specified file. See read_iolog. Specify a separate file for each job, otherwise the iologs will be interspersed and the file may be corrupt. This file will be opened in append mode.

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 (`blkparse <device> -o /dev/null -d file_for_fio.bin'). You can specify a number of files by separating the names with a ':' character. See the filename option for information on how to escape ':' characters within the file names. These files will be sequentially assigned to job clones created by numjobs. '-' is a reserved name, meaning read from stdin, notably if filename is set to '-' which means stdin as well, then this flag can't be set to '-'.

read_iolog_chunked=bool

Determines how iolog is read. If false (default) entire read_iolog will be read at once. If selected true, input from iolog will be read gradually. Useful when iolog is very large, or it is generated.

merge_blktrace_file=str

When specified, rather than replaying the logs passed to read_iolog, the logs go through a merge phase which aggregates them into a single blktrace. The resulting file is then passed on as the read_iolog parameter. The intention here is to make the order of events consistent. This limits the influence of the scheduler compared to replaying multiple blktraces via concurrent jobs.

merge_blktrace_scalars=float_list

This is a percentage based option that is index paired with the list of files passed to read_iolog. When merging is performed, scale the time of each event by the corresponding amount. For example, `--merge_blktrace_scalars="50:100"' runs the first trace in halftime and the second trace in realtime. This knob is separately tunable from replay_time_scale which scales the trace during runtime and will not change the output of the merge unlike this option.

merge_blktrace_iters=float_list

This is a whole number option that is index paired with the list of files passed to read_iolog. When merging is performed, run each trace for the specified number of iterations. For example, `--merge_blktrace_iters="2:1"' runs the first trace for two iterations and the second trace for one iteration.

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_time_scale=int

When replaying I/O with read_iolog, fio will honor the original timing in the trace. With this option, it's possible to scale the time. It's a percentage option, if set to 50 it means run at 50% the original IO rate in the trace. If set to 200, run at twice the original IO rate. Defaults to 100.

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 different 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 single 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 the byte offsets in a trace to this value. The value must be a power of 2.

replay_scale=int

Scale bye offsets down by this factor when replaying traces. Should most likely use replay_align as well.

Threads, processes and job synchronization

replay_skip=str

Sometimes it's useful to skip certain IO types in a replay trace. This could be, for instance, eliminating the writes in the trace. Or not replaying the trims/discards, if you are redirecting to a device that doesn't support them. This option takes a comma separated list of read, write, trim, sync.

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 limitations. First, the waitee must be defined prior to the waiter job (meaning no forward 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 manpage for other operating systems since meaning of priority may differ. For per-command priority setting, see the I/O engine specific `cmdprio_percentage` and `cmdprio` options.

prioclass=int

Set the I/O priority class. See man ionice(1). For per-command priority setting, see the I/O engine specific `cmdprio_percentage` and `cmdprio_class` options.

priohint=int

Set the I/O priority hint. This is only applicable to platforms that support I/O priority classes and to devices with features controlled through priority hints, e.g. block devices supporting command duration limits, or CDL. CDL is a way to indicate the desired maximum latency of I/Os so that the device can optimize its internal command scheduling according to the latency limits indicated by the user. For per-I/O priority hint setting, see the I/O engine specific cmdprio_hint option.

cpus_allowed=str

Controls the same options as cpumask, but accepts a textual specification of the permitted CPUs instead and CPUs are indexed from 0. So to use CPUs 0 and 5 you would specify `cpus_allowed=0,5'. This option also allows a range of CPUs to be specified -- say you wanted a binding to CPUs 0, 5, and 8 to 15, you would set `cpus_allowed=0,5,8-15'.

cpus_allowed_policy=str

Set the policy of how fio distributes the CPUs specified by cpus_allowed or cpumask. Two policies are supported:

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.

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:

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:

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 fio regulates the activity between two or more jobs sharing the same flow_id. Fio attempts to keep each job activity proportional to other jobs' activities in the same flow_id group, with respect to requested weight per job. That is, if one job has `flow=3', another job has `flow=2' and another with `flow=1`, then there will be a roughly 3:2:1 ratio in how much one runs vs the others.

flow_sleep=int

The period of time, in microseconds, to wait after the flow counter has exceeded its proportion 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. Optionally you can use `stonewall=0` to disable or `stonewall=1` to enable it.

exitall

By default, fio will continue running all other jobs when one job finishes. Sometimes this is not the desired action. Setting exitall will instead make fio terminate all jobs in the same group, as soon as one job of that group finishes.

exit_what=str

By default, fio will continue running all other jobs when one job finishes. Sometimes this is not the desired action. Setting exitall will instead make fio terminate all jobs in the same group. The option exit_what allows you to control which jobs get terminated when exitall is enabled. The default value is group. The allowed values are:

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 invocation 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. verify can be combined with verify_pattern option. The allowed values are:

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 pattern 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 supports %o format, which means that for each block offset will be written and then verified back, e.g.:

verify_fatal=bool

Normally fio will keep checking the entire contents before quitting on a block verification 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:

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.

experimental_verify=bool

Enable experimental verification. Standard verify records I/O metadata for later use during the verification phase. Experimental verify instead resets the file after the write phase and then replays I/Os for the verification phase.

verify_write_sequence=bool

Verify the header write sequence number. In a scenario with multiple jobs, verification of the write sequence number may fail. Disabling this option will mean that write sequence number checking is skipped. Doing that can be useful for testing atomic writes, as it means that checksum verification can still be attempted. For when atomic is enabled, checksum verification is expected to succeed (while write sequence checking can still fail).

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.

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.

Measurements and reporting

per_job_logs=bool

If set to true, fio generates bw/clat/iops logs with per job unique filenames. If set to false, jobs with identical names will share a log filename. Note that when this option is set to false log files will be opened in append mode and if log files already exist the previous contents will not be overwritten. 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.

write_lat_log=str

Same as write_bw_log, except this option creates I/O submission (e.g., `name_slat.x.log'), completion (e.g., `name_clat.x.log'), and total (e.g., `name_lat.x.log') latency files instead. See write_bw_log for details about the filename format and the LOG FILE FORMATS section for how data is structured within the files.

write_hist_log=str

Same as write_bw_log but writes an I/O completion latency histogram file (e.g., `name_hist.x.log') instead. Note that this file will be empty unless log_hist_msec has also been set. See write_bw_log for details about the filename format and the LOG FILE FORMATS section for how data is structured within the file.

write_iops_log=str

Same as write_bw_log, but writes an IOPS file (e.g. `name_iops.x.log`) instead. Because fio defaults to individual I/O logging, the value entry in the IOPS log will be 1 unless windowed logging (see log_avg_msec) has been enabled. See write_bw_log for details about the filename format and LOG FILE FORMATS for how data is structured within the file.

log_entries=int

By default, fio will log an entry in the iops, latency, or bw log for every I/O that completes. The initial number of I/O log entries is 1024. When the log entries are all used, new log entries are dynamically allocated. This dynamic log entry allocation may negatively impact time-related statistics such as I/O tail latencies (e.g. 99.9th percentile completion latency). This option allows specifying a larger initial number of log entries to avoid run-time allocation of new log entries, resulting in more precise time-related I/O statistics. Also see log_avg_msec as well. Defaults to 1024.

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 directs fio to instead record an average over the specified duration for each log entry, reducing the resolution of the log. When the job completes, fio will flush any accumulated latency log data, so the final log interval may not match the value specified by this option and there may even be duplicate timestamps. See log_window_value as well. Defaults to 0, logging entries for each I/O. 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 and write_hist_log as well. Defaults to 0, meaning histogram logging is disabled.

log_hist_coarseness=int

Integer ranging from 0 to 6, defining the coarseness of the resolution of the histogram logs enabled with log_hist_msec. For each increment in coarseness, fio outputs half as many bins. Defaults to 0, for which histogram logs contain 1216 latency bins. See LOG FILE FORMATS section.

log_window_value=str, log_max_value=str

If log_avg_msec is set, fio by default logs the average over that window. This option determines whether fio logs the average, maximum or both the values over the window. This only affects the latency logging, as both average and maximum values for iops or bw log will be same. Accepted values are:

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_prio=bool

If this is set, the `Command priority` field in LOG FILE FORMATS shows the priority value and the IO priority class of the command. Otherwise, the field shows if the command has the highest RT priority class or not. Also see LOG FILE FORMATS section.

log_issue_time=bool

If this is set, the iolog options will include the command issue time for the I/O entry as well as the other data values. Defaults to 0 meaning that command issue times are not present in logs. Also see LOG FILE FORMATS section. This option shall be set together with write_lat_log and log_offset.

log_compression=int

If this is set, fio will compress the I/O logs as it goes, to keep the memory footprint lower. When a log reaches the specified size, that chunk is removed and compressed 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. See cpus_allowed for the format used.

log_store_compressed=bool

If set, fio will store the log files in a compressed format. They can be decompressed with fio, using the --inflate-log command line parameter. The files will be stored with a `.fz' suffix.

log_unix_epoch=bool

Backward-compatible alias for log_alternate_epoch.

log_alternate_epoch=bool

If set, fio will log timestamps based on the epoch used by the clock specified in the log_alternate_epoch_clock_id option, to the log files produced by enabling write_type_log for each log type, instead of the default zero-based timestamps.

log_alternate_epoch_clock_id=int

Specifies the clock_id to be used by clock_gettime to obtain the alternate epoch if log_alternate_epoch is true. Otherwise has no effect. Default value is 0, or CLOCK_REALTIME.

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 milliseconds. 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 milliseconds. 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.

slat_percentiles=bool

Report submission latency percentiles. Submission latency is not recorded for synchronous ioengines.

clat_percentiles=bool

Report completion latency percentiles.

lat_percentiles=bool

Report total latency percentiles. Total latency is the sum of submission latency and completion latency.

percentile_list=float_list

Overwrite the default list of percentiles for latencies and the block error histogram. Each number is a floating point number in the range (0,100], and the maximum length of the list is 20. Use ':' to separate the numbers. For example, `--percentile_list=99.5:99.9' will cause fio to report the latency durations below which 99.5% and 99.9% of the observed latencies fell, respectively.

significant_figures=int

If using --output-format of `normal', set the significant figures to this value. Higher values will yield more precise IOPS and throughput units, while lower values will round. Requires a minimum value of 1 and a maximum value of 10. Defaults to 4.

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.

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:

To view a profile's additional options use --cmdhelp after specifying the profile. For example:

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.