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 matching the I/O load one wants to simulate.

--debug =type Enable verbose tracing of various fio actions. May be `all' for all types or individual types separated by a comma (eg --debug=io,file). `help' will list all available tracing options.

--output =filename Write output to filename.

--output-format =format Set the reporting format to normal, terse, or json.

--runtime =runtime Limit run time to runtime seconds.

--bandwidth-log Generate per-job bandwidth logs.

--minimal Print statistics in a terse, semicolon-delimited format.

--append-terse Print statistics in selected mode AND terse, semicolon-delimited format.

--version Display version information and exit.

--terse-version =version Set terse version output format (Current version 3, or older version 2).

--help Display usage information and exit.

--cpuclock-test Perform test and validation of internal CPU clock

--crctest[=test] Test the speed of the builtin checksumming functions. If no argument is given, all of them are tested. Or 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.

--showcmd =jobfile Convert jobfile to a set of command-line options.

--eta =when Specifies when real-time ETA estimate should be printed. when may be one of `always', `never' or `auto'.

--eta-newline =time Force an ETA newline for every `time` period passed.

--status-interval =time Report full output status every `time` period passed.

--readonly Turn on safety read-only checks, preventing any attempted write.

--section =sec Only run section sec from job file. This option can be used multiple times to add more sections to run.

--alloc-size =kb Set the internal smalloc pool size to kb kilobytes.

--warnings-fatal All fio parser warnings are fatal, causing fio to exit with an error.

--max-jobs =nr Set the maximum allowed number of jobs (threads/processes) to support.

--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 pid file.

--client =host Instead of running the jobs locally, send and run them on the given host.

--idle-prof =option Report cpu idleness on a system or percpu basis (option=system,percpu) or run unit work calibration only (option=calibrate).

Job files are in `ini' format. They consist of one or more job definitions, which begin with a job name in square brackets and extend to the next job name. The job name can be any ASCII string except `global', which has a special meaning. Following the job name is a sequence of zero or more parameters, one per line, that define the behavior of the job. Any line starting with a `;' or `#' character is considered a comment and ignored.

If jobfile is specified as `-', the job file will be read from standard input.

The global section contains default parameters for jobs specified in the job file. A job is only affected by global sections residing above it, and there may be any number of global sections. Specific job definitions may override any parameter set in global sections. Some parameters may take arguments of a specific type. Anywhere a numeric value is required, an arithmetic expression may be used, provided it is surrounded by parentheses. Supported operators are:

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 types used are:

str String: a sequence of alphanumeric characters.

int SI integer: a whole number, possibly containing a suffix denoting the base unit of the value. Accepted suffixes are `k', 'M', 'G', 'T', and 'P', denoting kilo (1024), mega (1024^2), giga (1024^3), tera (1024^4), and peta (1024^5) respectively. If prefixed with '0x', the value is assumed to be base 16 (hexadecimal). A suffix may include a trailing 'b', for instance 'kb' is identical to 'k'. You can specify a base 10 value by using 'KiB', 'MiB','GiB', etc. This is useful for disk drives where values are often given in base 10 values. Specifying '30GiB' will get you 30*1000^3 bytes. When specifying times the default suffix meaning changes, still denoting the base unit of the value, but accepted suffixes are 'D' (days), 'H' (hours), 'M' (minutes), 'S' Seconds, 'ms' (or msec) milli seconds, 'us' (or 'usec') micro seconds. Time values without a unit specify seconds. The suffixes are not case sensitive.

bool Boolean: a true or false value. `0' denotes false, `1' denotes true.

irange Integer range: a range of integers specified in the format lower:upper or lower-upper. lower and upper may contain a suffix as described above. If an option allows two sets of ranges, they are separated with a `,' or `/' character. For example: `8-8k/8M-4G'.

float_list List of floating numbers: A list of floating numbers, separated by a ':' character.

name =str May be used to override the job name. On the command line, this parameter has the special purpose of signalling the start of a new job.

description =str Human-readable description of the job. It is printed when the job is run, but otherwise has no special purpose.

directory =str Prefix filenames with this directory. Used to place files in a location other 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 creates with 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 each clone if not specified, but let all clones use the same if set. See filename for considerations regarding escaping certain characters on some platforms.

filename =str fio normally makes up a file name based on the job name, thread number, and file number. If you want to share files between threads in a job or several jobs, specify a filename for each of them to override the default. If the I/O engine is file-based, you can specify a number of files by separating the names with a `:' character. `-' is a reserved name, meaning stdin or stdout, depending on the read/write direction set. On Windows, disk devices are accessed as \\.\PhysicalDrive0 for the first device, \\.\PhysicalDrive1 for the second etc. Note: Windows and FreeBSD prevent write access to areas of the disk containing in-use data (e.g. filesystems). If the wanted filename does need to include a colon, then escape that with a '\\' character. For instance, if the filename is "/dev/dsk/foo@3,0:c", then you would use filename="/dev/dsk/foo@3,0\\:c".

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:

lockfile =str Fio defaults to not locking any files before it does IO to them. If a file or file descriptor is shared, fio can serialize IO to that file to make the end result consistent. This is usual for emulating real workloads that share files. The lock modes are:

opendir =str Recursively open any files below directory str.

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 IO offset being generated. Accepted values are:

kb_base =int The base unit for a kilobyte. The defacto base is 2^10, 1024. Storage manufacturers like to use 10^3 or 1000 as a base ten unit instead, for obvious reasons. Allowed values are 1024 or 1000, with 1024 being the default.

unified_rw_reporting =bool Fio normally reports statistics on a per data direction basis, meaning that read, write, and trim are accounted and reported separately. If this option is set fio sums the results and reports 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:

fadvise_hint =bool Use posix_fadvise\|(2) to advise the kernel what I/O patterns are likely to be issued. Default: true.

size =int Total size of I/O for this job. fio will run until this many bytes have been transferred, unless limited by other options (runtime, for instance, or increased/descreased by io_size). Unless nrfiles and filesize options are given, this amount will be divided between the available files for the job. If not set, 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.

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 IO to be performed. Sometimes that is not what you want. With this option, it is possible to define just the amount of IO that fio should do. For instance, if size is set to 20G and io_limit is set to 5G, fio will perform IO within the first 20G but exit when 5G have been done. The opposite is also possible - if size is set to 20G, and io_size is set to 40G, then fio will do 40G of IO within the 0..20G region.

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 IO 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.

filesize =irange Individual file sizes. May be a range, in which case fio will select sizes for files at random within the given range, limited to size in total (if that is given). If filesize is not specified, each created file is the same size.

file_append =bool Perform IO 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.

blocksize =int[,int] ", bs" =int[,int] Block size for I/O units. Default: 4k. Values for reads, writes, and trims can be specified separately in the format read,write,trim either of which may be empty to leave that value at its default. If a trailing comma isn't given, the remainder will inherit the last value set.

blocksize_range =irange[,irange] ", bsrange" =irange[,irange] Specify a range of I/O block sizes. The issued I/O unit will always be a multiple of the minimum size, unless blocksize_unaligned is set. Applies to both reads and writes if only one range is given, but can be specified separately with a comma separating the values. Example: bsrange=1k-4k,2k-8k. Also (see blocksize).

bssplit =str This option allows even finer grained control of the block sizes issued, not just even splits between them. With this option, you can weight various block sizes for exact control of the issued IO for a job that has mixed block sizes. The format of the option is bssplit=blocksize/percentage, optionally adding as many definitions as needed separated by a colon. Example: bssplit=4k/10:64k/50:32k/40 would issue 50% 64k blocks, 10% 4k blocks and 40% 32k blocks. bssplit also supports giving separate splits to reads and writes. The format is identical to what the bs option accepts, the read and write parts are separated with a comma.

blocksize_unaligned, bs_unaligned If set, any size in blocksize_range may be used. This typically won't work with direct I/O, as that normally requires sector alignment.

blockalign =int[,int] ", ba" =int[,int] At what boundary to align random IO offsets. Defaults to the same as 'blocksize' the minimum blocksize given. Minimum alignment is typically 512b for using direct IO, 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.

bs_is_seq_rand =bool If this option is set, fio will use the normal read,write blocksize settings as sequential,random instead. Any random read or write will use the WRITE blocksize settings, and any sequential read or write will use the READ blocksize setting.

zero_buffers Initialize buffers with all zeros. Default: fill buffers with random data. The resulting IO buffers will not be completely zeroed, unless scramble_buffers is also turned off.

refill_buffers If this option is given, fio will refill the IO 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 IO 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 IO buffer content (on WRITEs) that compress to the specified level. Fio does this by providing a mix of random data and a fixed pattern. The fixed pattern is either zeroes, or the pattern specified by buffer_pattern. If the pattern option is used, it might skew the compression ratio slightly. Note that this is per block size unit, for file/disk wide compression level that matches this setting. Note that this is per block size unit, for file/disk wide compression 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 buffer_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 IO buffer.

buffer_pattern =str If set, fio will fill the IO buffers with this pattern. If not set, the contents of IO buffers is 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 "".

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.

nrfiles =int Number of files to use for this job. Default: 1.

openfiles =int Number of files to keep open at the same time. Default: nrfiles.

file_service_type =str Defines how files to service are selected. The following types are defined:

ioengine =str Defines how the job issues I/O. The following types are defined:

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 degress 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 IO is not async on that OS. Keep an eye on the IO depth distribution in the fio output to verify that the achieved depth is as expected. Default: 1.

iodepth_batch =int Number of I/Os to submit at once. Default: iodepth.

iodepth_batch_complete =int This defines how many pieces of IO to retrieve at once. It defaults to 1 which means that we'll ask for a minimum of 1 IO in the retrieval process from the kernel. The IO 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 IO. This helps reduce IO latency, at the cost of more retrieval system calls.

iodepth_low =int Low watermark indicating when to start filling the queue again. Default: iodepth.

direct =bool If true, use non-buffered I/O (usually O_DIRECT). Default: false.

atomic =bool If value is true, attempt to use atomic direct IO. Atomic writes are guaranteed to be stable once acknowledged by the operating system. Only Linux supports O_ATOMIC right now.

buffered =bool If true, use buffered I/O. This is the opposite of the direct parameter. Default: true.

offset =int Offset in the file to start I/O. Data before the offset will not be touched.

offset_increment =int If this is provided, then the real offset becomes the 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.

number_ios =int Fio will normally perform IOs 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 IOs to perform. When fio reaches this number, it will exit normally and report status. Note that this does not extend the amount of IO that will be done, it will only stop fio if this condition is met before other end-of-job criteria.

fsync =int How many I/Os to perform before issuing an fsync\|(2) of dirty data. If 0, don't sync. Default: 0.

fdatasync =int Like fsync, but uses fdatasync\|(2) instead to only sync the data parts of the file. Default: 0.

write_barrier =int Make every Nth write a barrier write.

sync_file_range =str:int Use sync_file_range\|(2) for every val 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:

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 writing, setup the file first and do overwrites. Default: false.

end_fsync =bool Sync file contents when a write stage has completed. Default: false.

fsync_on_close =bool If true, sync file contents on close. This differs from end_fsync in that it will happen on every 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 rwmixread and rwmixwrite are given and do not sum to 100%, the latter of the two overrides 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 By default, fio will use a completely uniform random distribution when asked to perform random IO. 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:

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, genzipf, that can be used visualize 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.

percentage_random =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. It is possible to set different values for reads, writes, and trim. To do so, simply use a comma separated list. See blocksize.

norandommap Normally fio will cover every block of the file when doing random I/O. If this parameter is given, a new offset will be chosen without looking at past I/O history. This parameter is mutually exclusive with verify.

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 IO offsets for random IO:

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 guarantees that we never generate the same offset twice, and it's also less computationally expensive. It's not a true random generator, however, though for IO purposes it's typically good enough. LFSR only works with single block sizes, not with workloads that use multiple block sizes. If used with such a workload, fio may read or write some blocks multiple times.

nice =int Run job with given nice value. See nice\|(2).

prio =int Set I/O priority value of this job between 0 (highest) and 7 (lowest). See ionice\|(1).

prioclass =int Set I/O priority class. See ionice\|(1).

thinktime =int Stall job for given number of microseconds between issuing I/Os.

thinktime_spin =int Pretend to spend CPU time for given number of microseconds, sleeping the rest of the time specified by thinktime. Only valid if thinktime is set.

thinktime_blocks =int Only valid if thinktime is set - control how many blocks to issue, before waiting thinktime microseconds. If not set, defaults to 1 which will make fio wait thinktime microseconds after every block. This effectively makes any queue depth setting redundant, since no more than 1 IO 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. Default: 1.

rate =int Cap bandwidth used by this job. The number is in bytes/sec, the normal postfix rules apply. You can use rate=500k to limit reads and writes to 500k each, or you can specify read and writes separately. Using rate=1m,500k would limit reads to 1MB/sec and writes to 500KB/sec. Capping only reads or writes can be done with rate=,500k or rate=500k,. The former will only limit writes (to 500KB/sec), the latter will only limit reads.

ratemin =int Tell fio to do whatever it can to maintain at least the given bandwidth. Failing to meet this requirement will cause the job to exit. The same format as rate is used for read vs write separation.

rate_iops =int Cap the bandwidth to this number of IOPS. Basically the same as rate, just specified independently of bandwidth. The same format as rate is used for read vs write separation. If blocksize is a range, the smallest block size is used as the metric.

rate_iops_min =int If this rate of I/O is not met, the job will exit. The same format as rate is used for read vs write separation.

ratecycle =int Average bandwidth for rate and ratemin over this number of milliseconds. Default: 1000ms.

latency_target =int 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. The values is given in microseconds. See latency_window and latency_percentile.

latency_window =int Used with latency_target to specify the sample window that the job is run at varying queue depths to test the performance. The value is given in microseconds.

latency_percentile =float The percentage of IOs that must fall within the criteria specified by latency_target and latency_window. If not set, this defaults to 100.0, meaning that all IOs must be equal or below to the value set by latency_target.

max_latency =int If set, fio will exit the job if it exceeds this maximum latency. It will exit with an ETIME error.

cpumask =int Set CPU affinity for this job. int is a bitmask of allowed CPUs the job may run on. See sched_setaffinity\|(2).

cpus_allowed =str Same as cpumask, but allows a comma-delimited list of CPU numbers.

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

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'.

numa_mem_policy =str Set this job's memory policy and corresponding NUMA nodes. Format of the arguments:

For default and local memory policy, no nodelist is needed to be specified. For prefer, only one node is allowed. For bind and interleave, nodelist allows comma delimited list of numbers, A-B ranges, or 'all'.

startdelay =irange Delay start of job for the specified number of seconds. Supports all time suffixes to allow specification of hours, minutes, seconds and milliseconds - seconds are the default if a unit is omitted. Can be given as a range which causes each thread to choose randomly out of the range.

runtime =int Terminate processing after the specified number of seconds.

time_based If given, run for the specified runtime duration even if the files are completely read or written. The same workload will be repeated as many times as runtime allows.

ramp_time =int 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.

invalidate =bool Invalidate buffer-cache for the file prior to starting I/O. Default: true.

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 Allocation method for I/O unit buffer. Allowed values are:

iomem_align =int ", mem_align" =int This indicates the memory alignment of the IO memory buffers. Note that the given alignment is applied to the first IO 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 IO memory buffers is the sum of the iomem_align and bs used.

hugepage-size =int Defines the size of a huge page. Must be at least equal to the system setting. Should be a multiple of 1MB. Default: 4MB.

exitall Terminate all jobs when one finishes. Default: wait for each job to finish.

bwavgtime =int Average bandwidth calculations over the given time in milliseconds. Default: 500ms.

iopsavgtime =int Average IOPS calculations over the given time in milliseconds. Default: 500ms.

create_serialize =bool If true, serialize file creation for the jobs. Default: true.

create_fsync =bool fsync\|(2) data file after creation. Default: true.

create_on_open =bool If true, the files are not created until they are opened for IO by the job.

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.

pre_read =bool If this is given, files will be pre-read into memory before starting the given IO 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 IO engines that are seekable, since they allow you to read the same data multiple times. Thus it will not work on eg network or splice IO.

unlink =bool Unlink job files when done. Default: false.

loops =int Specifies the number of iterations (runs of the same workload) of this job. Default: 1.

verify_only =bool Do not perform the 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 Method of verifying file contents after each iteration of the job. Allowed values are:

verifysort =bool If true, written verify blocks are sorted if fio deems it to be faster to read them back in a sorted manner. 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 for this number of bytes, which should divide blocksize. Default: blocksize.

verify_pattern =str If set, fio will fill the io buffers with this pattern. Fio defaults to filling with totally random bytes, but sometimes it's interesting to fill with a known pattern for io 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=meta.

verify_fatal =bool If true, exit the job on the first observed verification 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 IO inline from the submitting thread. This option takes an integer describing how many async offload threads to create for IO verification instead, causing fio to offload the duty of verifying IO contents to one or more separate threads. If using this offload option, even sync IO engines can benefit from using an iodepth setting higher than 1, as it allows them to have IO in flight while verifies are running.

verify_async_cpus =str Tell fio to set the given CPU affinity on the async IO 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 IO 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.

trim_percentage =int Number of verify blocks to discard/trim.

trim_verify_zero =bool Verify that trim/discarded blocks are returned as zeroes.

trim_backlog =int Trim after this number of blocks are written.

trim_backlog_batch =int Trim this number of IO blocks.

experimental_verify =bool Enable experimental verification.

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.

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.

stonewall ", wait_for_previous" Wait for preceding jobs in the job file to exit before starting this one. stonewall implies new_group.

new_group Start a new reporting group. If not given, all jobs in a file will be part of the same reporting group, unless separated by a stonewall.

numjobs =int Number of clones (processes/threads performing the same workload) of this job. Default: 1.

group_reporting If set, display per-group reports instead of per-job when numjobs is specified.

thread Use threads created with pthread_create\|(3) instead of processes created with fork\|(2).

zonesize =int Divide file into zones of the specified size in bytes. See zoneskip.

zonerange =int Give size of an IO zone. See zoneskip.

zoneskip =int Skip the specified number of bytes when zonesize bytes of data have been read.

write_iolog =str Write the issued I/O patterns to the specified file. Specify a separate file for each job, otherwise the iologs will be interspersed and the file may be corrupt.

read_iolog =str Replay the I/O patterns contained in the specified file generated by write_iolog, or may be a blktrace binary file.

replay_no_stall =int While replaying I/O patterns using read_iolog the default behavior attempts to respect timing information between I/Os. Enabling replay_no_stall causes I/Os to be replayed as fast as possible while still respecting ordering.

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. Setting replay_redirect causes all IOPS to be replayed onto the single specified device regardless of the device it was recorded from.

write_bw_log =str If given, write a bandwidth log of the jobs in this job file. 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 behaviour 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)

write_lat_log =str Same as write_bw_log, but writes I/O completion latencies. 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.

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.

log_avg_msec =int By default, fio will log an entry in the iops, latency, or bw log for every IO 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. Defaults to 0.

log_offset =bool If this is set, the iolog options will include the byte offset for the IO entry as well as the other data values.

log_compression =int If this is set, fio will compress the IO 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 IO 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 IO 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_store_compressed =bool If set, and log_compression is also 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.

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 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 measurements of throughput/bandwidth numbers. See disable_lat.

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.

exec_prerun =str Before running the job, execute the specified command with system\|(3).

exec_postrun =str Same as exec_prerun, but the command is executed after the job completes.

ioscheduler =str Attempt to switch the device hosting the file to the specified I/O scheduler.

disk_util =bool Generate disk utilization statistics if the platform supports it. Default: true.

clocksource =str Use the given clocksource as the base of timing. The supported options are:

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) 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 gtod() 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 IO 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.

ignore_error =str Sometimes you want to ignore some errors during test in that case you can specify error list for each error type.

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 an integer.

Example: ignore_error=EAGAIN,ENOSPC:122 .

This option will ignore EAGAIN from READ, and ENOSPC and 122(EDQUOT) from WRITE.

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

profile =str Select a specific builtin performance test.

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

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.

unit_base =int Base unit for reporting. Allowed values are:

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

clat_percentiles =bool Enable the reporting of percentiles of completion latencies.

percentile_list =float_list Overwrite the default list of percentiles for completion latencies. 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. 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.

Some parameters 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.

(cpu)cpuload =int Attempt to use the specified percentage of CPU cycles.

(cpu)cpuchunks =int Split the load into cycles of the given time. In microseconds.

(cpu)exit_on_io_done =bool Detect when IO threads are done, then exit.

(libaio)userspace_reap Normally, with the libaio engine in use, fio will use the io_getevents 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 (eg when iodepth_batch_complete=0).

(net,netsplice)hostname =str The host name or IP address to use for TCP or UDP based IO. 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.

(net,netsplice)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.

(net,netsplice)interface =str The IP address of the network interface used to send or receive UDP multicast packets.

(net,netsplice)ttl =int Time-to-live value for outgoing UDP multicast packets. Default: 1

(net,netsplice)nodelay =bool Set TCP_NODELAY on TCP connections.

(net,netsplice)protocol =str ", proto" =str The network protocol to use. Accepted values are:

(net,netsplice)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.

(net, pingpong) =bool Normally a network writer will just continue writing data, and a network reader will just consume packets. 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.

(net, window_size) =int Set the desired socket buffer size for the connection.

(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 block allocation strategy

(rbd)rbdname =str Specifies the name of the RBD.

(rbd)pool =str Specifies the name of the Ceph pool containing the RBD.

(rbd)clientname =str Specifies the username (without the 'client.' prefix) used to access the Ceph cluster.

While running, fio will display the status of the created jobs. For example:

The characters in the first set of brackets denote the current status of each threads. The possible values are:

0

The second set of brackets shows the estimated completion percentage of the current group. The third set shows the read and write I/O rate, respectively. Finally, the estimated run time of the job is displayed.

When fio completes (or is interrupted by Ctrl-C), it will show data for each thread, each group of threads, and each disk, in that order.

Per-thread statistics first show the threads client number, group-id, and error code. The remaining figures are as follows:

The group statistics show:

0

Finally, disk statistics are printed with reads first:

0

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.

If the --minimal / --append-terse options are given, the results will be printed/appended in a semicolon-delimited format suitable for scripted use. A job description (if provided) follows on a new line. Note that the first number in the line is the version number. If the output has to be changed for some reason, this number will be incremented by 1 to signify that change. The fields are:

Normally you would run fio as a stand-alone application on the machine where the IO workload should be generated. However, it is also possible to run the frontend and backend of fio separately. This makes it possible to have a fio server running on the machine(s) where the IO workload should be running, while controlling it from another machine. To start the server, you would do: fio --server=args on that machine, 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=1.2.3.4 Start a fio server, listening on IP 1.2.3.4 on the default port. 6) fio --server=sock:/tmp/fio.sock Start a fio server, listening on the local socket /tmp/fio.sock. When a server is running, you can connect to it from a client. The client is run with: fio --local-args --client=server --remote-args <job file(s)> where --local-args are arguments that are local to the client where it is running, 'server' is the connect 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. You can connect to multiple clients as well, to do that you could run: fio --client=server2 --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 the fio serer will open this local (to the server) job file instead of being passed one from the client. fio was written by Jens Axboe <jens.axboe@oracle.com>, now Jens Axboe <axboe@fb.com>.

This man page was written by Aaron Carroll <aaronc@cse.unsw.edu.au> based on documentation by Jens Axboe.

Report bugs to the fio mailing list <fio@vger.kernel.org>. See README. For further documentation see HOWTO and README.

Sample jobfiles are available in the examples directory.