fio(1)                      General Commands Manual                     fio(1)

       fio - flexible I/O tester

       fio [options] [jobfile]...

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

              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

              Write output to filename.

              Set the reporting format to normal, terse, json, or json+.
              Multiple formats can be selected, separate by a comma. terse is
              a CSV based format. json+ is like json, except it adds a full
              dump of the latency buckets.

              Limit run time to runtime seconds.

              Generate per-job bandwidth logs.

              Print statistics in a terse, semicolon-delimited format.

              Print statistics in selected mode AND terse, semicolon-delimited
              format.  Deprecated, use --output-format instead to select
              multiple formats.

              Display version information and exit.

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

       --help Display usage information and exit.

              Perform test and validation of internal CPU clock

              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.

              Print help information for command.  May be `all' for all

              List all commands defined by ioengine, or print help for command
              defined by ioengine.

              Convert jobfile to a set of command-line options.

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

              Force an ETA newline for every `time` period passed.

              Report full output status every `time` period passed.

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

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

              Set the internal smalloc pool size to kb kilobytes.

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

              Set the maximum allowed number of jobs (threads/processes) to

              Start a backend server, with args specifying what to listen to.
              See client/server section.

              Background a fio server, writing the pid to the given pid file.

              Instead of running the jobs locally, send and run them on the
              given host or set of hosts.  See client/server section.

              Report cpu idleness on a system or percpu basis
              (option=system,percpu) or run unit work calibration only

       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

   Global Section
       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:

                     addition (+)

                     subtraction (-)

                     multiplication (*)

                     division (/)

                     modulus (%)

                     exponentiation (^)

       For time values in expressions, units are microseconds by default. This
       is different than for time values not in expressions (not enclosed in
       parentheses). The 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

       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:

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

   Parameter List
              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.

              Specifies the name of the already defined job to wait for.
              Single waitee name only may be specified. If set, the job won't
              be started until all workers of the 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).

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

              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

              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

              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:

                            The name of the worker thread or process.

                            The incremental number of the worker thread or

                            The incremental number of the file for that worker
                            thread or process.

              To have dependent jobs share a set of files, this option can be
              set to have fio generate filenames that are shared between the
              two. For instance, if testfiles.$filenum is specified, file
              number 4 for any job will be named testfiles.4. The default of
              $jobname.$jobnum.$filenum will be used if no other format
              specifier is given.

              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:

                     none   No locking. This is the default.

                            Only one thread or process may do IO at a time,
                            excluding all others.

                            Read-write locking on the file. Many readers may
                            access the file at the same time, but writes get
                            exclusive access.

       opendir=str Recursively open any files below directory str.

       readwrite=str, rw=str
              Type of I/O pattern.  Accepted values are:

                     read   Sequential reads.

                     write  Sequential writes.

                     trim   Sequential trim (Linux block devices only).

                            Random reads.

                            Random writes.

                            Random trim (Linux block devices only).

                     rw, readwrite
                            Mixed sequential reads and writes.

                     randrw Mixed random reads and writes.

                            Trim and write mixed workload. Blocks will be
                            trimmed first, then the same blocks will be
                            written to.

              For mixed I/O, the default split is 50/50. For certain types of
              io the result may still be skewed a bit, since the speed may be
              different. It is possible to specify a number of IO's to do
              before getting a new offset, this is done by appending a `:<nr>
              to the end of the string given. For a random read, it would look
              like rw=randread:8 for passing in an offset modifier with a
              value of 8. If the postfix is used with a sequential IO pattern,
              then the value specified will be added to the generated offset
              for each IO. For instance, using rw=write:4k will skip 4k for
              every write. It turns sequential IO into sequential IO with
              holes. See the rw_sequencer option.

              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:

                            Generate sequential offset

                            Generate the same offset

              sequential is only useful for random IO, where fio would
              normally generate a new random offset for every IO. If you
              append eg 8 to randread, you would get a new random offset for
              every 8 IO's. The result would be a seek for only every 8 IO's,
              instead of for every IO. Use rw=randread:8 to specify that. As
              sequential IO is already sequential, setting sequential for that
              would not result in any differences.  identical behaves in a
              similar fashion, except it sends the same offset 8 number of
              times before generating a new offset.

              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.

              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.

              Seed the random number generator used for random I/O patterns in
              a predictable way so the pattern is repeatable across runs.
              Default: true.

              Seed all random number generators in a predictable way so
              results are repeatable across runs.  Default: false.

              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

              Whether pre-allocation is performed when laying down files.
              Accepted values are:

                     none   Do not pre-allocate space.

                     posix  Pre-allocate via posix_fallocate(3).

                     keep   Pre-allocate via fallocate(2) with
                            FALLOC_FL_KEEP_SIZE set.

                     0      Backward-compatible alias for 'none'.

                     1      Backward-compatible alias for 'posix'.

              May not be available on all supported platforms. 'keep' is only
              available on Linux. If using ZFS on Solaris this must be set to
              'none' because ZFS doesn't support it. Default: 'posix'.

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

              Use posix_fadvise(2) to advise the kernel what stream ID the
              writes issued belong to. Only supported on Linux. Note, this
              option may change going forward.

              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

       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.

              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.

              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).

              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

       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

       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.

              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.

              Initialize buffers with all zeros. Default: fill buffers with
              random data.

              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.

              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.

              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.

              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.

              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 "",

              Also you can combine everything together in any order:


              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.

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

              Number of files to keep open at the same time.  Default:

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

                     random Choose a file at random.

                            Round robin over opened files (default).

                            Do each file in the set sequentially.

              The number of I/Os to issue before switching to a new file can
              be specified by appending `:int' to the service type.

              Defines how the job issues I/O.  The following types are

                     sync   Basic read(2) or write(2) I/O.  fseek(2) is used
                            to position the I/O location.

                     psync  Basic pread(2) or pwrite(2) I/O.

                     vsync  Basic readv(2) or writev(2) I/O. Will emulate
                            queuing by coalescing adjacent IOs into a single

                     pvsync Basic preadv(2) or pwritev(2) I/O.

                            Basic preadv2(2) or pwritev2(2) I/O.

                     libaio Linux native asynchronous I/O. This ioengine
                            defines engine specific options.

                            POSIX asynchronous I/O using aio_read(3) and

                            Solaris native asynchronous I/O.

                            Windows native asynchronous I/O.

                     mmap   File is memory mapped with mmap(2) and data copied
                            using memcpy(3).

                     splice splice(2) is used to transfer the data and
                            vmsplice(2) to transfer data from user-space to
                            the kernel.

                            Use the syslet system calls to make regular
                            read/write asynchronous.

                     sg     SCSI generic sg v3 I/O. May be either synchronous
                            using the SG_IO ioctl, or if the target is an sg
                            character device, we use read(2) and write(2) for
                            asynchronous I/O.

                     null   Doesn't transfer any data, just pretends to.
                            Mainly used to exercise fio itself and for
                            debugging and testing purposes.

                     net    Transfer over the network.  The protocol to be
                            used can be defined with the protocol parameter.
                            Depending on the protocol, filename, hostname,
                            port, or listen must be specified.  This ioengine
                            defines engine specific options.

                            Like net, but uses splice(2) and vmsplice(2) to
                            map data and send/receive. This ioengine defines
                            engine specific options.

                     cpuio  Doesn't transfer any data, but burns CPU cycles
                            according to cpuload and cpucycles parameters.

                     guasi  The GUASI I/O engine is the Generic Userspace
                            Asynchronous Syscall Interface approach to
                            asynchronous I/O.
                            See <>.

                     rdma   The RDMA I/O engine supports both RDMA memory
                            semantics (RDMA_WRITE/RDMA_READ) and channel
                            semantics (Send/Recv) for the InfiniBand, RoCE and
                            iWARP protocols.

                            Loads an external I/O engine object file.  Append
                            the engine filename as `:enginepath'.

                               IO engine that does regular linux native
                            fallocate call to simulate data transfer as fio
                              DDIR_READ  does fallocate(,mode =
                              DIR_WRITE does fallocate(,mode = 0)
                              DDIR_TRIM does fallocate(,mode =

                            IO engine that does regular EXT4_IOC_MOVE_EXT
                            ioctls to simulate defragment activity request to
                            DDIR_WRITE event

                     rbd    IO engine supporting direct access to Ceph Rados
                            Block Devices (RBD) via librbd without the need to
                            use the kernel rbd driver. This ioengine defines
                            engine specific options.

                     gfapi  Using Glusterfs libgfapi sync interface to direct
                            access to Glusterfs volumes without having to go
                            through FUSE. This ioengine defines engine
                            specific options.

                            Using Glusterfs libgfapi async interface to direct
                            access to Glusterfs volumes without having to go
                            through FUSE. This ioengine defines engine
                            specific options.

                            Read and write through Hadoop (HDFS).  The
                            filename option is used to specify host,port of
                            the hdfs name-node to connect. This engine
                            interprets offsets a little differently. In HDFS,
                            files once created cannot be modified.  So random
                            writes are not possible. To imitate this, libhdfs
                            engine expects bunch of small files to be created
                            over HDFS, and engine will randomly pick a file
                            out of those files based on the offset generated
                            by fio backend. (see the example job file to
                            create such files, use rw=write option). Please
                            note, you might want to set necessary environment
                            variables to work with hdfs/libhdfs properly.

                     mtd    Read, write and erase an MTD character device
                            (e.g., /dev/mtd0). Discards are treated as erases.
                            Depending on the underlying device type, the I/O
                            may have to go in a certain pattern, e.g., on
                            NAND, writing sequentially to erase blocks and
                            discarding before overwriting. The writetrim mode
                            works well for this constraint.

              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, iodepth_batch_submit=int
              This defines how many pieces of IO to submit at once. It
              defaults to 1 which means that we submit each IO as soon as it
              is available, but can be raised to submit bigger batches of IO
              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 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.

              This defines maximum pieces of IO 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 IO which should be retrieved. By default
              it is equal to iodepth_batch_complete_min value.

              Example #1:


              which means that we will retrieve at leat 1 IO and up to the
              whole submitted queue depth. If none of IO has been completed
              yet, we will wait.

              Example #2:


              which means that we can retrieve up to the whole submitted queue
              depth, but if none of IO has been completed yet, we will NOT
              wait and immediately exit the system call. In this example we
              simply do polling.

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

              This option controls how fio submits the IO to the IO engine.
              The default is inline, which means that the fio job threads
              submit and reap IO directly.  If set to offload, the job threads
              will offload IO submission to a dedicated pool of IO threads.
              This requires some coordination and thus has a bit of extra
              overhead, especially for lower queue depth IO 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 IO gets back up on the
              device side (the coordinated omission problem).

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

              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.

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

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

              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.

              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.

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

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

              Make every Nth write a barrier write.

              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:


              write  SYNC_FILE_RANGE_WRITE


              So if you do sync_file_range=wait_before,write:8, fio
              would use
              writes.  Also see the sync_file_range(2) man page.  This option
              is Linux specific.

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

              Sync file contents when a write stage has completed.  Default:

              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.

              Percentage of a mixed workload that should be reads. Default:

              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.

              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:

              random Uniform random distribution

              zipf   Zipf distribution

              pareto Pareto distribution

              gauss  Normal (gaussian) distribution

              zoned  Zoned random distribution

              When using a zipf or pareto distribution, an input value
              is also
              needed to define the access pattern. For zipf, this is the zipf
              theta.  For pareto, it's the pareto power. Fio includes a test
              program, 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. For the
              gauss distribution, a normal deviation is supplied as a value
              between 0 and 100.

              For a zoned distribution, fio supports specifying percentages of
              IO access that should fall within what range of the file or
              device. For example, given a criteria of:

                     60% of accesses should be to the first 10%
                     30% of accesses should be to the next 20%
                     8% of accesses should be to to the next 30%
                     2% of accesses should be to the next 40%

              we can define that through zoning of the random accesses. For
              the above example, the user would do:


              similarly to how bssplit works for setting ranges and
              percentages of block sizes. Like bssplit, it's possible to
              specify separate zones for reads, writes, and trims. If just one
              set is given, it'll apply to all of them.

              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.

              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.

              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

              Fio supports the following engines for generating IO offsets for
              random IO:

                     Strong 2^88 cycle random number generator

              lfsr   Linear feedback shift register generator

                     Strong 64-bit 2^258 cycle random number generator

              Tausworthe is a strong random number generator, but it
              requires tracking on the
              side if we want to ensure that blocks are only read or written
              once. LFSR 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. The default value is tausworthe, unless the required
              space exceeds 2^32 blocks. If it does, then tausworthe64 is
              selected automatically.

              Run job with given nice value.  See nice(2).

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

              Set I/O priority class.  See ionice(1).

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

              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.

              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.

              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.

              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

              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.

              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.

              This option controls how fio manages rated IO submissions. The
              default is linear, which submits IO in a linear fashion with
              fixed delays between IOs that gets adjusted based on IO
              completion rates. If this is set to poisson, fio will submit IO
              based on a more real world random request flow, known as the
              Poisson process (
              The lambda will be 10^6 / IOPS for the given workload.

              Average bandwidth for rate and rate_min over this number of
              milliseconds.  Default: 1000ms.

              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.

              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.

              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.

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

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

              Same as cpumask, but allows a comma-delimited list of CPU

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

                     shared All jobs will share the CPU set specified.

                     split  Each job will get a unique CPU from the CPU set.

              shared is the default behaviour, if the option isn't specified.
              If split is specified, then fio will assign one cpu per job. If
              not enough CPUs are given for the jobs listed, then fio will
              roundrobin the CPUs in the set.

              Set this job running on specified NUMA nodes' CPUs. The
              arguments allow comma delimited list of cpu numbers, A-B ranges,
              or 'all'.

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


              mode   is one of the following memory policy:

              default, prefer, bind, interleave, local

              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'.

              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.

              Terminate processing after the specified number of seconds.

              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.

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

              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:

                     malloc Allocate memory with malloc(3).

                     shm    Use shared memory buffers allocated through

                            Same as shm, but use huge pages as backing.

                     mmap   Use mmap(2) for allocation.  Uses anonymous memory
                            unless a filename is given after the option in the
                            format `:file'.

                            Same as mmap, but use huge files as backing.

                            Same as mmap, but use a MMAP_SHARED mapping.

              The amount of memory allocated is the maximum allowed blocksize
              for the job multiplied by iodepth.  For shmhuge or mmaphuge to
              work, the system must have free huge pages allocated.  mmaphuge
              also needs to have hugetlbfs mounted, and file must point there.
              At least on Linux, huge pages must be manually allocated. See
              /proc/sys/vm/nr_hugehages and the documentation for that.
              Normally you just need to echo an appropriate number, eg echoing
              8 will ensure that the OS has 8 huge pages ready for use.

       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.

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

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

       exitall_on_error =bool
              Terminate all jobs if one job finishes in error.  Default: wait
              for each job to finish.

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

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

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

              fsync(2) data file after creation.  Default: true.

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

              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.

              If true, fio is permitted to create files as part of its
              workload. This is the default behavior. If this option is false,
              then fio will error out if the files it needs to use don't
              already exist. Default: true.

              If this isn't set, fio will abort jobs that are destructive (eg
              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. Default: false.

              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 job files when done.  Default: false.

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

              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.

              Run the verify phase after a write phase.  Only valid if verify
              is set.  Default: true.

              Method of verifying 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=str can be combined with verify_pattern=str option.  The
              allowed values are:

                     md5 crc16 crc32 crc32c crc32c-intel crc64 crc7 sha256
                     sha512 sha1 xxhash
                            Store appropriate checksum in the header of each
                            block. crc32c-intel is hardware accelerated SSE4.2
                            driven, falls back to regular crc32c if not
                            supported by the system.

                     meta   This option is deprecated, since now meta
                            information is included in generic verification
                            header and meta verification happens by default.
                            For detailed information see the description of
                            the verify=str setting. This option is kept
                            because of compatibility's sake with old
                            configurations. Do not use it.

                            Verify a strict pattern. Normally fio includes a
                            header with some basic information and
                            checksumming, but if this option is set, only the
                            specific pattern set with verify_pattern is

                     null   Pretend to verify.  Used for testing internals.

              This option can be used for repeated burn-in tests of a system
              to make sure that the written data is also correctly read back.
              If the data direction given is a read or random read, fio will
              assume that it should verify a previously written file. If the
              data direction includes any form of write, the verify will be of
              the newly written data.

              If true, written verify blocks are sorted if fio deems it to be
              faster to read them back in a sorted manner.  Default: true.

              Pre-load and sort verify blocks for a read workload.

              Swap the verification header with data somewhere else in the
              block before writing.  It is swapped back before verifying.

              Write the verification header for this number of bytes, which
              should divide blocksize.  Default: blocksize.

              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=str. Also, verify_pattern
              supports %o format, which means that for each block offset will
              be written and then verifyied back, e.g.:
              Or use combination of everything:


              If true, exit the job on the first observed verification
              failure.  Default: false.

              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.

              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

              Tell fio to set the given CPU affinity on the async IO
              verification threads.  See cpus_allowed for the format used.

              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

              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.

              Number of verify blocks to discard/trim.

              Verify that trim/discarded blocks are returned as zeroes.

              Trim after this number of blocks are written.

              Trim this number of IO blocks.

              Enable experimental verification.

              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.

              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.

              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

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

              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).

              Divide file into zones of the specified size in bytes.  See

              Give size of an IO zone.  See zoneskip.

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

              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.

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

              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.

              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.

              Force alignment of IO offsets and lengths in a trace to this
              power of 2 value.

              Scale sector offsets down by this factor when replaying traces.

              If set, this generates bw/clat/iops log with per file private
              filenames. If not set, jobs with identical names will share the
              log filename. Default: true.

              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). If per_job_logs is false, then the filename
              will not include the job index. See the LOG FILE FORMATS

              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. If per_job_logs is
              false, then the filename will not include the job index. See the
              LOG FILE FORMATS section.

              Same as write_bw_log, but writes IOPS. If no filename is given
              with this option, the default filename of "jobname_type.x.log"
              is used, where x is the index of the job (1..N, where N is the
              number of jobs). Even if the filename is given, fio will still
              append the type of log. If per_job_logs is false, then the
              filename will not include the job index. See the LOG FILE
              FORMATS section.

              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. See log_max_value
              as well.  Defaults to 0, logging all entries.

              If log_avg_msec is set, fio logs the average over that window.
              If you instead want to log the maximum value, set this option to
              1.  Defaults to 0, meaning that averaged values are logged.

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

              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.

              Define the set of CPUs that are allowed to handle online log
              compression for the IO jobs. This can provide better isolation
              between performance sensitive jobs, and background compression

              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

              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.

              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 measurements of completion latency numbers. See

              Disable measurements of submission latency numbers. See

              Disable measurements of throughput/bandwidth numbers. See

              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.

              Before running the job, execute the specified command with
              Output is redirected in a file called jobname.prerun.txt

              Same as exec_prerun, but the command is executed after the job
              Output is redirected in a file called jobname.postrun.txt

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

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

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



              cpu    Internal CPU clock source

              cpu is the preferred clocksource if it is reliable, as it
              is very fast
              (and fio is heavy on time calls). Fio will automatically use
              this clocksource if it's supported and considered reliable on
              the system it is running on, unless another clocksource is
              specifically set. For x86/x86-64 CPUs, this means supporting TSC

              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

              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.

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

              If set dump every error even if it is non fatal, true by
              default. If disabled only fatal error will be dumped

              Select a specific builtin performance test.

              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

              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.

              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

              Instead of running as the invoking user, set the user ID to this
              value before the thread/process does any work.

              Set group ID, see uid.

              Base unit for reporting.  Allowed values are:

              0      Use auto-detection (default).

              8      Byte based.

              1      Bit based.

              The ID of the flow. If not specified, it defaults to being a
              global flow. See flow.

              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.

              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.

              The period of time, in microseconds, to wait after the flow
              watermark has been exceeded before retrying operations

              Enable the reporting of percentiles of completion latencies.

              Overwrite the default list of percentiles for completion
              latencies and the block error histogram. Each number is a
              floating number in the range (0,100], and the maximum length of
              the list is 20. Use ':' to separate the numbers. 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.

   Ioengine Parameters List
       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.

              Attempt to use the specified percentage of CPU cycles.

              Split the load into cycles of the given time. In microseconds.

              Detect when IO threads are done, then exit.

              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

              Set RWF_HIPRI on IO, indicating to the kernel that it's of
              higher priority than normal.

              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

              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.

              The IP address of the network interface used to send or receive
              UDP multicast packets.

              Time-to-live value for outgoing UDP multicast packets. Default:

              Set TCP_NODELAY on TCP connections.

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

                     tcp    Transmission control protocol

                     tcpv6  Transmission control protocol V6

                     udp    User datagram protocol

                     udpv6  User datagram protocol V6

                     unix   UNIX domain socket

              When the protocol is TCP or UDP, the port must also be given, as
              well as the hostname if the job is a TCP listener or UDP reader.
              For unix sockets, the normal filename option should be used and
              the port is invalid.

              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.

              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.

              Set the desired socket buffer size for the connection.

              Set the TCP maximum segment size (TCP_MAXSEG).

              File will be used as a block donor (swap extents between files)

              Configure donor file block allocation strategy
              0(default): Preallocate donor's file on init

              1:     allocate space immediately inside defragment event, and
                     free right after event

              Specifies the name of the RBD.

              Specifies the name of the Ceph pool containing the RBD.

              Specifies the username (without the 'client.' prefix) used to
              access the Ceph cluster.

              Skip operations against known bad blocks.

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

              Threads: 1: [_r] [24.8% done] [ 13509/  8334 kb/s] [eta

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

              P      Setup but not started.
              C      Thread created.
              I      Initialized, waiting.
              R      Running, doing sequential reads.
              r      Running, doing random reads.
              W      Running, doing sequential writes.
              w      Running, doing random writes.
              M      Running, doing mixed sequential reads/writes.
              m      Running, doing mixed random reads/writes.
              F      Running, currently waiting for fsync(2).
              V      Running, verifying written data.
              E      Exited, not reaped by main thread.
              -      Exited, thread reaped.

       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:

              io     Number of megabytes of I/O performed.

              bw     Average data rate (bandwidth).

              runt   Threads run time.

              slat   Submission latency minimum, maximum, average and standard
                     deviation. This is the time it took to submit the I/O.

              clat   Completion latency minimum, maximum, average and standard
                     deviation.  This is the time between submission and

              bw     Bandwidth minimum, maximum, percentage of aggregate
                     bandwidth received, average and standard deviation.

              cpu    CPU usage statistics. Includes user and system time,
                     number of context switches this thread went through and
                     number of major and minor page faults. The CPU
                     utilization numbers are averages for the jobs in that
                     reporting group, while the context and fault counters are

              IO depths
                     Distribution of I/O depths.  Each depth includes
                     everything less than (or equal) to it, but greater than
                     the previous depth.

              IO issued
                     Number of read/write requests issued, and number of short
                     read/write requests.

              IO latencies
                     Distribution of I/O completion latencies.  The numbers
                     follow the same pattern as IO depths.

       The group statistics show:
              io     Number of megabytes I/O performed.
              aggrb  Aggregate bandwidth of threads in the group.
              minb   Minimum average bandwidth a thread saw.
              maxb   Maximum average bandwidth a thread saw.
              mint   Shortest runtime of threads in the group.
              maxt   Longest runtime of threads in the group.

       Finally, disk statistics are printed with reads first:
              ios    Number of I/Os performed by all groups.
              merge  Number of merges in the I/O scheduler.
              ticks  Number of ticks we kept the disk busy.
                     Total time spent in the disk queue.
              util   Disk utilization.

       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

       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:

              terse version, fio version, jobname, groupid, error

              Read status:
                     Total I/O (KB), bandwidth (KB/s), IOPS, runtime (ms)

                     Submission latency:
                            min, max, mean, standard deviation
                     Completion latency:
                            min, max, mean, standard deviation
                     Completion latency percentiles (20 fields):
                            Xth percentile=usec
                     Total latency:
                            min, max, mean, standard deviation
                            min, max, aggregate percentage of total, mean,
                            standard deviation

              Write status:
                     Total I/O (KB), bandwidth (KB/s), IOPS, runtime (ms)

                     Submission latency:
                            min, max, mean, standard deviation
                     Completion latency:
                            min, max, mean, standard deviation
                     Completion latency percentiles (20 fields):
                            Xth percentile=usec
                     Total latency:
                            min, max, mean, standard deviation
                            min, max, aggregate percentage of total, mean,
                            standard deviation

              CPU usage:
                     user, system, context switches, major page faults, minor
                     page faults

              IO depth distribution:
                     <=1, 2, 4, 8, 16, 32, >=64

              IO latency distribution:
                            <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000
                            <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000,
                            2000, >=2000

              Disk utilization (1 for each disk used):
                     name, read ios, write ios, read merges, write merges,
                     read ticks, write ticks, read in-queue time, write in-
                     queue time, disk utilization percentage

              Error Info (dependent on continue_on_error, default off):
                     total # errors, first error code

              text description (if provided in config - appears on newline)

       There are two trace file format that you can encounter. The older (v1)
       format is unsupported since version 1.20-rc3 (March 2008). It will
       still be described below in case that you get an old trace and want to
       understand it.

       In any case the trace is a simple text file with a single action per

       Trace file format v1
              Each line represents a single io action in the following format:

              rw, offset, length

              where rw=0/1 for read/write, and the offset and length entries
              being in bytes.

              This format is not supported in Fio versions => 1.20-rc3.

       Trace file format v2
              The second version of the trace file format was added in Fio
              version 1.17.  It allows to access more then one file per trace
              and has a bigger set of possible file actions.

              The first line of the trace file has to be:

              fio version 2 iolog

              Following this can be lines in two different formats, which are
              described below.  The file management format:

              filename action

              The filename is given as an absolute path. The action can be one
              of these:

                     add    Add the given filename to the trace
                     open   Open the file with the given filename. The
                            filename has to have been previously added with
                            the add action.
                     close  Close the file with the given filename. The file
                            must have previously been opened.

              The file io action format:

              filename action offset length

              The filename is given as an absolute path, and has to have been
              added and opened before it can be used with this format. The
              offset and length are given in bytes. The action can be one of

                     wait   Wait for 'offset' microseconds. Everything below
                            100 is discarded.  The time is relative to the
                            previous wait statement.
                     read   Read length bytes beginning from offset
                     write  Write length bytes beginning from offset
                     sync   fsync() the file
                            fdatasync() the file
                     trim   trim the given file from the given offset for
                            length bytes

       In some cases, we want to understand CPU overhead in a test. For
       example, we test patches for the specific goodness of whether they
       reduce CPU usage.  fio implements a balloon approach to create a thread
       per CPU that runs at idle priority, meaning that it only runs when
       nobody else needs the cpu.  By measuring the amount of work completed
       by the thread, idleness of each CPU can be derived accordingly.

       An unit work is defined as touching a full page of unsigned characters.
       Mean and standard deviation of time to complete an unit work is
       reported in "unit work" section. Options can be chosen to report
       detailed percpu idleness or overall system idleness by aggregating
       percpu stats.

       Fio is usually run in one of two ways, when data verification is done.
       The first is a normal write job of some sort with verify enabled. When
       the write phase has completed, fio switches to reads and verifies
       everything it wrote. The second model is running just the write phase,
       and then later on running the same job (but with reads instead of
       writes) to repeat the same IO patterns and verify the contents. Both of
       these methods depend on the write phase being completed, as fio
       otherwise has no idea how much data was written.

       With verification triggers, fio supports dumping the current write
       state to local files. Then a subsequent read verify workload can load
       this state and know exactly where to stop. This is useful for testing
       cases where power is cut to a server in a managed fashion, for

       A verification trigger consists of two things:

              Storing the write state of each job

              Executing a trigger command

       The write state is relatively small, on the order of hundreds of bytes
       to single kilobytes. It contains information on the number of
       completions done, the last X completions, etc.

       A trigger is invoked either through creation (touch) of a specified
       file in the system, or through a timeout setting. If fio is run with
       --trigger-file=/tmp/trigger-file, then it will continually check for
       the existence of /tmp/trigger-file. When it sees this file, it will
       fire off the trigger (thus saving state, and executing the trigger

       For client/server runs, there's both a local and remote trigger. If fio
       is running as a server backend, it will send the job states back to the
       client for safe storage, then execute the remote trigger, if specified.
       If a local trigger is specified, the server will still send back the
       write state, but the client will then execute the trigger.

       Verification trigger example

              Lets say we want to run a powercut test on the remote machine
              'server'.  Our write workload is in write-test.fio. We want to
              cut power to 'server' at some point during the run, and we'll
              run this test from the safety or our local machine, 'localbox'.
              On the server, we'll start the fio backend normally:

              server# fio --server

              and on the client, we'll fire off the workload:

              localbox$ fio --client=server --trigger-file=/tmp/my-trigger
              --trigger-remote="bash -c "echo b > /proc/sysrq-triger""

              We set /tmp/my-trigger as the trigger file, and we tell fio to

              echo b > /proc/sysrq-trigger

              on the server once it has received the trigger and sent us the
              write state. This will work, but it's not really cutting power
              to the server, it's merely abruptly rebooting it. If we have a
              remote way of cutting power to the server through IPMI or
              similar, we could do that through a local trigger command
              instead. Lets assume we have a script that does IPMI reboot of a
              given hostname, ipmi-reboot. On localbox, we could then have run
              fio with a local trigger instead:

              localbox$ fio --client=server --trigger-file=/tmp/my-trigger
              --trigger="ipmi-reboot server"

              For this case, fio would wait for the server to send us the
              write state, then execute 'ipmi-reboot server' when that

       Loading verify state
              To load store write state, read verification job file must
              contain the verify_state_load option. If that is set, fio will
              load the previously stored state. For a local fio run this is
              done by loading the files directly, and on a client/server run,
              the server backend will ask the client to send the files over
              and load them from there.

       Fio supports a variety of log file formats, for logging latencies,
       bandwidth, and IOPS. The logs share a common format, which looks like

       time (msec), value, data direction, offset

       Time for the log entry is always in milliseconds. The value logged
       depends on the type of log, it will be one of the following:

       Latency log
              Value is in latency in usecs
       Bandwidth log
              Value is in KB/sec
       IOPS log
              Value is in IOPS

       Data direction is one of the following:

       0      IO is a READ
       1      IO is a WRITE
       2      IO is a TRIM

       The offset is the offset, in bytes, from the start of the file, for
       that particular IO. The logging of the offset can be toggled with

       If windowed logging is enabled though log_avg_msec, then fio doesn't
       log individual IOs. Instead of logs the average values over the
       specified period of time. Since data direction and offset are per-IO
       values, they aren't applicable if windowed logging is enabled. If
       windowed logging is enabled and log_max_value is set, then fio logs
       maximum values in that window instead of averages.

       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

       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

       4) fio --server=,4444

          Start a fio server, listening on all interfaces on port 4444.

       5) fio --server=

          Start a fio server, listening on IP on the default port.

       6) fio --server=sock:/tmp/fio.sock

          Start a fio server, listening on the local socket /tmp/fio.sock.

       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-

       fio --client=server --remote-config /path/to/file.fio

       Then fio will open this local (to the server) job file instead of being
       passed one from the client.

       If you have many servers (example: 100 VMs/containers), you can input a
       pathname of a file containing host IPs/names as the parameter value for
       the --client option.  For example, here is an example "host.list" file
       containing 2 hostnames:


       The fio command would then be:

       fio --client=host.list <job file>

       In this mode, you cannot input server-specific parameters or job files,
       and all servers receive the same job file.

       In order to enable fio --client runs utilizing a shared filesystem from
       multiple hosts, fio --client now prepends the IP address of the server
       to the filename. For example, if fio is using directory /mnt/nfs/fio
       and is writing filename fileio.tmp, with a --client hostfile containing
       two hostnames h1 and h2 with IP addresses and, then fio will create two files:


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

       Report bugs to the fio mailing list <>.  See README.

       For further documentation see HOWTO and README.
       Sample jobfiles are available in the examples directory.

User Manual                      December 2014                          fio(1)