8 5. Detailed list of parameters
13 1.0 Overview and history
14 ------------------------
15 fio was originally written to save me the hassle of writing special test
16 case programs when I wanted to test a specific workload, either for
17 performance reasons or to find/reproduce a bug. The process of writing
18 such a test app can be tiresome, especially if you have to do it often.
19 Hence I needed a tool that would be able to simulate a given io workload
20 without resorting to writing a tailored test case again and again.
22 A test work load is difficult to define, though. There can be any number
23 of processes or threads involved, and they can each be using their own
24 way of generating io. You could have someone dirtying large amounts of
25 memory in an memory mapped file, or maybe several threads issuing
26 reads using asynchronous io. fio needed to be flexible enough to
27 simulate both of these cases, and many more.
31 The first step in getting fio to simulate a desired io workload, is
32 writing a job file describing that specific setup. A job file may contain
33 any number of threads and/or files - the typical contents of the job file
34 is a global section defining shared parameters, and one or more job
35 sections describing the jobs involved. When run, fio parses this file
36 and sets everything up as described. If we break down a job from top to
37 bottom, it contains the following basic parameters:
39 IO type Defines the io pattern issued to the file(s).
40 We may only be reading sequentially from this
41 file(s), or we may be writing randomly. Or even
42 mixing reads and writes, sequentially or randomly.
44 Block size In how large chunks are we issuing io? This may be
45 a single value, or it may describe a range of
48 IO size How much data are we going to be reading/writing.
50 IO engine How do we issue io? We could be memory mapping the
51 file, we could be using regular read/write, we
52 could be using splice, async io, syslet, or even
55 IO depth If the io engine is async, how large a queuing
56 depth do we want to maintain?
58 IO type Should we be doing buffered io, or direct/raw io?
60 Num files How many files are we spreading the workload over.
62 Num threads How many threads or processes should we spread
65 The above are the basic parameters defined for a workload, in addition
66 there's a multitude of parameters that modify other aspects of how this
72 See the README file for command line parameters, there are only a few
75 Running fio is normally the easiest part - you just give it the job file
76 (or job files) as parameters:
80 and it will start doing what the job_file tells it to do. You can give
81 more than one job file on the command line, fio will serialize the running
82 of those files. Internally that is the same as using the 'stonewall'
83 parameter described the the parameter section.
85 If the job file contains only one job, you may as well just give the
86 parameters on the command line. The command line parameters are identical
87 to the job parameters, with a few extra that control global parameters
88 (see README). For example, for the job file parameter iodepth=2, the
89 mirror command line option would be --iodepth 2 or --iodepth=2. You can
90 also use the command line for giving more than one job entry. For each
91 --name option that fio sees, it will start a new job with that name.
92 Command line entries following a --name entry will apply to that job,
93 until there are no more entries or a new --name entry is seen. This is
94 similar to the job file options, where each option applies to the current
95 job until a new [] job entry is seen.
97 fio does not need to run as root, except if the files or devices specified
98 in the job section requires that. Some other options may also be restricted,
99 such as memory locking, io scheduler switching, and decreasing the nice value.
104 As previously described, fio accepts one or more job files describing
105 what it is supposed to do. The job file format is the classic ini file,
106 where the names enclosed in [] brackets define the job name. You are free
107 to use any ascii name you want, except 'global' which has special meaning.
108 A global section sets defaults for the jobs described in that file. A job
109 may override a global section parameter, and a job file may even have
110 several global sections if so desired. A job is only affected by a global
111 section residing above it. If the first character in a line is a ';' or a
112 '#', the entire line is discarded as a comment.
114 So lets look at a really simple job file that define to threads, each
115 randomly reading from a 128MiB file.
117 ; -- start job file --
128 As you can see, the job file sections themselves are empty as all the
129 described parameters are shared. As no filename= option is given, fio
130 makes up a filename for each of the jobs as it sees fit. On the command
131 line, this job would look as follows:
133 $ fio --name=global --rw=randread --size=128m --name=job1 --name=job2
136 Lets look at an example that have a number of processes writing randomly
139 ; -- start job file --
151 Here we have no global section, as we only have one job defined anyway.
152 We want to use async io here, with a depth of 4 for each file. We also
153 increased the buffer size used to 32KiB and define numjobs to 4 to
154 fork 4 identical jobs. The result is 4 processes each randomly writing
155 to their own 64MiB file. Instead of using the above job file, you could
156 have given the parameters on the command line. For this case, you would
159 $ fio --name=random-writers --ioengine=libaio --iodepth=4 --rw=randwrite --bs=32k --direct=0 --size=64m --numjobs=4
161 fio ships with a few example job files, you can also look there for
165 5.0 Detailed list of parameters
166 -------------------------------
168 This section describes in details each parameter associated with a job.
169 Some parameters take an option of a given type, such as an integer or
170 a string. The following types are used:
172 str String. This is a sequence of alpha characters.
173 int Integer. A whole number value, can be negative. If prefixed with
174 0x, the integer is assumed to be of base 16 (hexidecimal).
175 siint SI integer. A whole number value, which may contain a postfix
176 describing the base of the number. Accepted postfixes are k/m/g,
177 meaning kilo, mega, and giga. So if you want to specify 4096,
178 you could either write out '4096' or just give 4k. The postfixes
179 signify base 2 values, so 1024 is 1k and 1024k is 1m and so on.
180 If the option accepts an upper and lower range, use a colon ':'
181 or minus '-' to seperate such values. See irange.
182 bool Boolean. Usually parsed as an integer, however only defined for
183 true and false (1 and 0).
184 irange Integer range with postfix. Allows value range to be given, such
185 as 1024-4096. A colon may also be used as the seperator, eg
186 1k:4k. If the option allows two sets of ranges, they can be
187 specified with a ',' or '/' delimiter: 1k-4k/8k-32k. Also see
190 With the above in mind, here follows the complete list of fio job
193 name=str ASCII name of the job. This may be used to override the
194 name printed by fio for this job. Otherwise the job
195 name is used. On the command line this parameter has the
196 special purpose of also signaling the start of a new
199 description=str Text description of the job. Doesn't do anything except
200 dump this text description when this job is run. It's
203 directory=str Prefix filenames with this directory. Used to places files
204 in a different location than "./".
206 filename=str Fio normally makes up a filename based on the job name,
207 thread number, and file number. If you want to share
208 files between threads in a job or several jobs, specify
209 a filename for each of them to override the default. If
210 the ioengine used is 'net', the filename is the host and
211 port to connect to in the format of =host/port. If the
212 ioengine is file based, you can specify a number of files
213 by seperating the names with a ':' colon. So if you wanted
214 a job to open /dev/sda and /dev/sdb as the two working files,
215 you would use filename=/dev/sda:/dev/sdb. '-' is a reserved
216 name, meaning stdin or stdout. Which of the two depends
217 on the read/write direction set.
219 opendir=str Tell fio to recursively add any file it can find in this
220 directory and down the file system tree.
222 lockfile=str Fio defaults to not doing any locking files before it does
223 IO to them. If a file or file descriptor is shared, fio
224 can serialize IO to that file to make the end result
225 consistent. This is usual for emulating real workloads that
226 share files. The lock modes are:
228 none No locking. The default.
229 exclusive Only one thread/process may do IO,
230 excluding all others.
231 readwrite Read-write locking on the file. Many
232 readers may access the file at the
233 same time, but writes get exclusive
236 The option may be post-fixed with a lock batch number. If
237 set, then each thread/process may do that amount of IOs to
238 the file before giving up the lock. Since lock acqusition is
239 expensive, batching the lock/unlocks will speed up IO.
242 rw=str Type of io pattern. Accepted values are:
244 read Sequential reads
245 write Sequential writes
246 randwrite Random writes
247 randread Random reads
248 rw Sequential mixed reads and writes
249 randrw Random mixed reads and writes
251 For the mixed io types, the default is to split them 50/50.
252 For certain types of io the result may still be skewed a bit,
253 since the speed may be different. It is possible to specify
254 a number of IO's to do before getting a new offset - this
255 is only useful for random IO, where fio would normally
256 generate a new random offset for every IO. If you append
257 eg 8 to randread, you would get a new random offset for
258 every 8 IO's. The result would be a seek for only every 8
259 IO's, instead of for every IO. Use rw=randread:8 to specify
262 randrepeat=bool For random IO workloads, seed the generator in a predictable
263 way so that results are repeatable across repetitions.
265 fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
266 on what IO patterns it is likely to issue. Sometimes you
267 want to test specific IO patterns without telling the
268 kernel about it, in which case you can disable this option.
269 If set, fio will use POSIX_FADV_SEQUENTIAL for sequential
270 IO and POSIX_FADV_RANDOM for random IO.
272 size=siint The total size of file io for this job. Fio will run until
273 this many bytes has been transferred, unless runtime is
274 limited by other options (such as 'runtime', for instance).
275 Unless specific nr_files and filesize options are given,
276 fio will divide this size between the available files
277 specified by the job.
279 filesize=siint Individual file sizes. May be a range, in which case fio
280 will select sizes for files at random within the given range
281 and limited to 'size' in total (if that is given). If not
282 given, each created file is the same size.
284 fill_device=bool Sets size to something really large and waits for ENOSPC (no
285 space left on device) as the terminating condition. Only makes
286 sense with sequential write.
289 bs=siint The block size used for the io units. Defaults to 4k. Values
290 can be given for both read and writes. If a single siint is
291 given, it will apply to both. If a second siint is specified
292 after a comma, it will apply to writes only. In other words,
293 the format is either bs=read_and_write or bs=read,write.
294 bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
295 for writes. If you only wish to set the write size, you
296 can do so by passing an empty read size - bs=,8k will set
297 8k for writes and leave the read default value.
299 blocksize_range=irange
300 bsrange=irange Instead of giving a single block size, specify a range
301 and fio will mix the issued io block sizes. The issued
302 io unit will always be a multiple of the minimum value
303 given (also see bs_unaligned). Applies to both reads and
304 writes, however a second range can be given after a comma.
307 bssplit=str Sometimes you want even finer grained control of the
308 block sizes issued, not just an even split between them.
309 This option allows you to weight various block sizes,
310 so that you are able to define a specific amount of
311 block sizes issued. The format for this option is:
313 bssplit=blocksize/percentage:blocksize/percentage
315 for as many block sizes as needed. So if you want to define
316 a workload that has 50% 64k blocks, 10% 4k blocks, and
317 40% 32k blocks, you would write:
319 bssplit=4k/10:64k/50:32k/40
321 Ordering does not matter. If the percentage is left blank,
322 fio will fill in the remaining values evenly. So a bssplit
323 option like this one:
325 bssplit=4k/50:1k/:32k/
327 would have 50% 4k ios, and 25% 1k and 32k ios. The percentages
328 always add up to 100, if bssplit is given a range that adds
329 up to more, it will error out.
332 bs_unaligned If this option is given, any byte size value within bsrange
333 may be used as a block range. This typically wont work with
334 direct IO, as that normally requires sector alignment.
336 zero_buffers If this option is given, fio will init the IO buffers to
337 all zeroes. The default is to fill them with random data.
339 refill_buffers If this option is given, fio will refill the IO buffers
340 on every submit. The default is to only fill it at init
341 time and reuse that data. Only makes sense if zero_buffers
342 isn't specified, naturally. If data verification is enabled,
343 refill_buffers is also automatically enabled.
345 nrfiles=int Number of files to use for this job. Defaults to 1.
347 openfiles=int Number of files to keep open at the same time. Defaults to
348 the same as nrfiles, can be set smaller to limit the number
351 file_service_type=str Defines how fio decides which file from a job to
352 service next. The following types are defined:
354 random Just choose a file at random.
356 roundrobin Round robin over open files. This
359 The string can have a number appended, indicating how
360 often to switch to a new file. So if option random:4 is
361 given, fio will switch to a new random file after 4 ios
364 ioengine=str Defines how the job issues io to the file. The following
367 sync Basic read(2) or write(2) io. lseek(2) is
368 used to position the io location.
370 psync Basic pread(2) or pwrite(2) io.
372 vsync Basic readv(2) or writev(2) IO.
374 libaio Linux native asynchronous io.
376 posixaio glibc posix asynchronous io.
378 mmap File is memory mapped and data copied
379 to/from using memcpy(3).
381 splice splice(2) is used to transfer the data and
382 vmsplice(2) to transfer data from user
385 syslet-rw Use the syslet system calls to make
386 regular read/write async.
388 sg SCSI generic sg v3 io. May either be
389 synchronous using the SG_IO ioctl, or if
390 the target is an sg character device
391 we use read(2) and write(2) for asynchronous
394 null Doesn't transfer any data, just pretends
395 to. This is mainly used to exercise fio
396 itself and for debugging/testing purposes.
398 net Transfer over the network to given host:port.
399 'filename' must be set appropriately to
400 filename=host/port regardless of send
401 or receive, if the latter only the port
404 netsplice Like net, but uses splice/vmsplice to
405 map data and send/receive.
407 cpuio Doesn't transfer any data, but burns CPU
408 cycles according to the cpuload= and
409 cpucycle= options. Setting cpuload=85
410 will cause that job to do nothing but burn
411 85% of the CPU. In case of SMP machines,
412 use numjobs=<no_of_cpu> to get desired CPU
413 usage, as the cpuload only loads a single
414 CPU at the desired rate.
416 guasi The GUASI IO engine is the Generic Userspace
417 Asyncronous Syscall Interface approach
420 http://www.xmailserver.org/guasi-lib.html
422 for more info on GUASI.
424 external Prefix to specify loading an external
425 IO engine object file. Append the engine
426 filename, eg ioengine=external:/tmp/foo.o
427 to load ioengine foo.o in /tmp.
429 iodepth=int This defines how many io units to keep in flight against
430 the file. The default is 1 for each file defined in this
431 job, can be overridden with a larger value for higher
434 iodepth_batch=int This defines how many pieces of IO to submit at once.
435 It defaults to 1 which means that we submit each IO
436 as soon as it is available, but can be raised to submit
437 bigger batches of IO at the time.
439 iodepth_low=int The low water mark indicating when to start filling
440 the queue again. Defaults to the same as iodepth, meaning
441 that fio will attempt to keep the queue full at all times.
442 If iodepth is set to eg 16 and iodepth_low is set to 4, then
443 after fio has filled the queue of 16 requests, it will let
444 the depth drain down to 4 before starting to fill it again.
446 direct=bool If value is true, use non-buffered io. This is usually
449 buffered=bool If value is true, use buffered io. This is the opposite
450 of the 'direct' option. Defaults to true.
452 offset=siint Start io at the given offset in the file. The data before
453 the given offset will not be touched. This effectively
454 caps the file size at real_size - offset.
456 fsync=int If writing to a file, issue a sync of the dirty data
457 for every number of blocks given. For example, if you give
458 32 as a parameter, fio will sync the file for every 32
459 writes issued. If fio is using non-buffered io, we may
460 not sync the file. The exception is the sg io engine, which
461 synchronizes the disk cache anyway.
463 overwrite=bool If true, writes to a file will always overwrite existing
464 data. If the file doesn't already exist, it will be
465 created before the write phase begins. If the file exists
466 and is large enough for the specified write phase, nothing
469 end_fsync=bool If true, fsync file contents when the job exits.
471 fsync_on_close=bool If true, fio will fsync() a dirty file on close.
472 This differs from end_fsync in that it will happen on every
473 file close, not just at the end of the job.
475 rwmixread=int How large a percentage of the mix should be reads.
477 rwmixwrite=int How large a percentage of the mix should be writes. If both
478 rwmixread and rwmixwrite is given and the values do not add
479 up to 100%, the latter of the two will be used to override
482 norandommap Normally fio will cover every block of the file when doing
483 random IO. If this option is given, fio will just get a
484 new random offset without looking at past io history. This
485 means that some blocks may not be read or written, and that
486 some blocks may be read/written more than once. This option
487 is mutually exclusive with verify= for that reason, since
488 fio doesn't track potential block rewrites which may alter
489 the calculated checksum for that block.
491 softrandommap See norandommap. If fio runs with the random block map enabled
492 and it fails to allocate the map, if this option is set it
493 will continue without a random block map. As coverage will
494 not be as complete as with random maps, this option is
497 nice=int Run the job with the given nice value. See man nice(2).
499 prio=int Set the io priority value of this job. Linux limits us to
500 a positive value between 0 and 7, with 0 being the highest.
503 prioclass=int Set the io priority class. See man ionice(1).
505 thinktime=int Stall the job x microseconds after an io has completed before
506 issuing the next. May be used to simulate processing being
507 done by an application. See thinktime_blocks and
511 Only valid if thinktime is set - pretend to spend CPU time
512 doing something with the data received, before falling back
513 to sleeping for the rest of the period specified by
517 Only valid if thinktime is set - control how many blocks
518 to issue, before waiting 'thinktime' usecs. If not set,
519 defaults to 1 which will make fio wait 'thinktime' usecs
522 rate=int Cap the bandwidth used by this job to this number of KiB/sec.
524 ratemin=int Tell fio to do whatever it can to maintain at least this
525 bandwidth. Failing to meet this requirement, will cause
528 rate_iops=int Cap the bandwidth to this number of IOPS. Basically the same
529 as rate, just specified independently of bandwidth. If the
530 job is given a block size range instead of a fixed value,
531 the smallest block size is used as the metric.
533 rate_iops_min=int If fio doesn't meet this rate of IO, it will cause
536 ratecycle=int Average bandwidth for 'rate' and 'ratemin' over this number
539 cpumask=int Set the CPU affinity of this job. The parameter given is a
540 bitmask of allowed CPU's the job may run on. So if you want
541 the allowed CPUs to be 1 and 5, you would pass the decimal
542 value of (1 << 1 | 1 << 5), or 34. See man
543 sched_setaffinity(2). This may not work on all supported
544 operating systems or kernel versions.
546 cpus_allowed=str Controls the same options as cpumask, but it allows a text
547 setting of the permitted CPUs instead. So to use CPUs 1 and
548 5, you would specify cpus_allowed=1,5.
550 startdelay=int Start this job the specified number of seconds after fio
551 has started. Only useful if the job file contains several
552 jobs, and you want to delay starting some jobs to a certain
555 runtime=int Tell fio to terminate processing after the specified number
556 of seconds. It can be quite hard to determine for how long
557 a specified job will run, so this parameter is handy to
558 cap the total runtime to a given time.
560 time_based If set, fio will run for the duration of the runtime
561 specified even if the file(s) are completey read or
562 written. It will simply loop over the same workload
563 as many times as the runtime allows.
565 invalidate=bool Invalidate the buffer/page cache parts for this file prior
566 to starting io. Defaults to true.
568 sync=bool Use sync io for buffered writes. For the majority of the
569 io engines, this means using O_SYNC.
572 mem=str Fio can use various types of memory as the io unit buffer.
573 The allowed values are:
575 malloc Use memory from malloc(3) as the buffers.
577 shm Use shared memory as the buffers. Allocated
580 shmhuge Same as shm, but use huge pages as backing.
582 mmap Use mmap to allocate buffers. May either be
583 anonymous memory, or can be file backed if
584 a filename is given after the option. The
585 format is mem=mmap:/path/to/file.
587 mmaphuge Use a memory mapped huge file as the buffer
588 backing. Append filename after mmaphuge, ala
589 mem=mmaphuge:/hugetlbfs/file
591 The area allocated is a function of the maximum allowed
592 bs size for the job, multiplied by the io depth given. Note
593 that for shmhuge and mmaphuge to work, the system must have
594 free huge pages allocated. This can normally be checked
595 and set by reading/writing /proc/sys/vm/nr_hugepages on a
596 Linux system. Fio assumes a huge page is 4MiB in size. So
597 to calculate the number of huge pages you need for a given
598 job file, add up the io depth of all jobs (normally one unless
599 iodepth= is used) and multiply by the maximum bs set. Then
600 divide that number by the huge page size. You can see the
601 size of the huge pages in /proc/meminfo. If no huge pages
602 are allocated by having a non-zero number in nr_hugepages,
603 using mmaphuge or shmhuge will fail. Also see hugepage-size.
605 mmaphuge also needs to have hugetlbfs mounted and the file
606 location should point there. So if it's mounted in /huge,
607 you would use mem=mmaphuge:/huge/somefile.
610 Defines the size of a huge page. Must at least be equal
611 to the system setting, see /proc/meminfo. Defaults to 4MiB.
612 Should probably always be a multiple of megabytes, so using
613 hugepage-size=Xm is the preferred way to set this to avoid
614 setting a non-pow-2 bad value.
616 exitall When one job finishes, terminate the rest. The default is
617 to wait for each job to finish, sometimes that is not the
620 bwavgtime=int Average the calculated bandwidth over the given time. Value
621 is specified in milliseconds.
623 create_serialize=bool If true, serialize the file creating for the jobs.
624 This may be handy to avoid interleaving of data
625 files, which may greatly depend on the filesystem
626 used and even the number of processors in the system.
628 create_fsync=bool fsync the data file after creation. This is the
631 unlink=bool Unlink the job files when done. Not the default, as repeated
632 runs of that job would then waste time recreating the fileset
635 loops=int Run the specified number of iterations of this job. Used
636 to repeat the same workload a given number of times. Defaults
639 do_verify=bool Run the verify phase after a write phase. Only makes sense if
640 verify is set. Defaults to 1.
642 verify=str If writing to a file, fio can verify the file contents
643 after each iteration of the job. The allowed values are:
645 md5 Use an md5 sum of the data area and store
646 it in the header of each block.
648 crc64 Use an experimental crc64 sum of the data
649 area and store it in the header of each
652 crc32 Use a crc32 sum of the data area and store
653 it in the header of each block.
655 crc16 Use a crc16 sum of the data area and store
656 it in the header of each block.
658 crc7 Use a crc7 sum of the data area and store
659 it in the header of each block.
661 sha512 Use sha512 as the checksum function.
663 sha256 Use sha256 as the checksum function.
665 meta Write extra information about each io
666 (timestamp, block number etc.). The block
669 null Only pretend to verify. Useful for testing
670 internals with ioengine=null, not for much
673 This option can be used for repeated burn-in tests of a
674 system to make sure that the written data is also
677 verifysort=bool If set, fio will sort written verify blocks when it deems
678 it faster to read them back in a sorted manner. This is
679 often the case when overwriting an existing file, since
680 the blocks are already laid out in the file system. You
681 can ignore this option unless doing huge amounts of really
682 fast IO where the red-black tree sorting CPU time becomes
685 verify_offset=siint Swap the verification header with data somewhere else
686 in the block before writing. Its swapped back before
689 verify_interval=siint Write the verification header at a finer granularity
690 than the blocksize. It will be written for chunks the
691 size of header_interval. blocksize should divide this
694 verify_pattern=int If set, fio will fill the io buffers with this
695 pattern. Fio defaults to filling with totally random
696 bytes, but sometimes it's interesting to fill with a known
697 pattern for io verification purposes. Depending on the
698 width of the pattern, fio will fill 1/2/3/4 bytes of the
699 buffer at the time. The verify_pattern cannot be larger than
702 verify_fatal=bool Normally fio will keep checking the entire contents
703 before quitting on a block verification failure. If this
704 option is set, fio will exit the job on the first observed
707 stonewall Wait for preceeding jobs in the job file to exit, before
708 starting this one. Can be used to insert serialization
709 points in the job file. A stone wall also implies starting
710 a new reporting group.
712 new_group Start a new reporting group. If this option isn't given,
713 jobs in a file will be part of the same reporting group
714 unless seperated by a stone wall (or if it's a group
715 by itself, with the numjobs option).
717 numjobs=int Create the specified number of clones of this job. May be
718 used to setup a larger number of threads/processes doing
719 the same thing. We regard that grouping of jobs as a
722 group_reporting If 'numjobs' is set, it may be interesting to display
723 statistics for the group as a whole instead of for each
724 individual job. This is especially true of 'numjobs' is
725 large, looking at individual thread/process output quickly
726 becomes unwieldy. If 'group_reporting' is specified, fio
727 will show the final report per-group instead of per-job.
729 thread fio defaults to forking jobs, however if this option is
730 given, fio will use pthread_create(3) to create threads
733 zonesize=siint Divide a file into zones of the specified size. See zoneskip.
735 zoneskip=siint Skip the specified number of bytes when zonesize data has
736 been read. The two zone options can be used to only do
737 io on zones of a file.
739 write_iolog=str Write the issued io patterns to the specified file. See
742 read_iolog=str Open an iolog with the specified file name and replay the
743 io patterns it contains. This can be used to store a
744 workload and replay it sometime later. The iolog given
745 may also be a blktrace binary file, which allows fio
746 to replay a workload captured by blktrace. See blktrace
747 for how to capture such logging data. For blktrace replay,
748 the file needs to be turned into a blkparse binary data
749 file first (blktrace <device> -d file_for_fio.bin).
751 write_bw_log If given, write a bandwidth log of the jobs in this job
752 file. Can be used to store data of the bandwidth of the
753 jobs in their lifetime. The included fio_generate_plots
754 script uses gnuplot to turn these text files into nice
757 write_lat_log Same as write_bw_log, except that this option stores io
758 completion latencies instead.
760 lockmem=siint Pin down the specified amount of memory with mlock(2). Can
761 potentially be used instead of removing memory or booting
762 with less memory to simulate a smaller amount of memory.
764 exec_prerun=str Before running this job, issue the command specified
767 exec_postrun=str After the job completes, issue the command specified
770 ioscheduler=str Attempt to switch the device hosting the file to the specified
771 io scheduler before running.
773 cpuload=int If the job is a CPU cycle eater, attempt to use the specified
774 percentage of CPU cycles.
776 cpuchunks=int If the job is a CPU cycle eater, split the load into
777 cycles of the given time. In milliseconds.
779 disk_util=bool Generate disk utilization statistics, if the platform
780 supports it. Defaults to on.
783 6.0 Interpreting the output
784 ---------------------------
786 fio spits out a lot of output. While running, fio will display the
787 status of the jobs created. An example of that would be:
789 Threads: 1: [_r] [24.8% done] [ 13509/ 8334 kb/s] [eta 00h:01m:31s]
791 The characters inside the square brackets denote the current status of
792 each thread. The possible values (in typical life cycle order) are:
796 P Thread setup, but not started.
798 I Thread initialized, waiting.
799 R Running, doing sequential reads.
800 r Running, doing random reads.
801 W Running, doing sequential writes.
802 w Running, doing random writes.
803 M Running, doing mixed sequential reads/writes.
804 m Running, doing mixed random reads/writes.
805 F Running, currently waiting for fsync()
806 V Running, doing verification of written data.
807 E Thread exited, not reaped by main thread yet.
810 The other values are fairly self explanatory - number of threads
811 currently running and doing io, rate of io since last check (read speed
812 listed first, then write speed), and the estimated completion percentage
813 and time for the running group. It's impossible to estimate runtime of
814 the following groups (if any).
816 When fio is done (or interrupted by ctrl-c), it will show the data for
817 each thread, group of threads, and disks in that order. For each data
818 direction, the output looks like:
820 Client1 (g=0): err= 0:
821 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
822 slat (msec): min= 0, max= 136, avg= 0.03, stdev= 1.92
823 clat (msec): min= 0, max= 631, avg=48.50, stdev=86.82
824 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, stdev=681.68
825 cpu : usr=1.49%, sys=0.25%, ctx=7969, majf=0, minf=17
826 IO depths : 1=0.1%, 2=0.3%, 4=0.5%, 8=99.0%, 16=0.0%, 32=0.0%, >32=0.0%
827 submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
828 complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
829 issued r/w: total=0/32768, short=0/0
830 lat (msec): 2=1.6%, 4=0.0%, 10=3.2%, 20=12.8%, 50=38.4%, 100=24.8%,
831 lat (msec): 250=15.2%, 500=0.0%, 750=0.0%, 1000=0.0%, >=2048=0.0%
833 The client number is printed, along with the group id and error of that
834 thread. Below is the io statistics, here for writes. In the order listed,
837 io= Number of megabytes io performed
838 bw= Average bandwidth rate
839 runt= The runtime of that thread
840 slat= Submission latency (avg being the average, stdev being the
841 standard deviation). This is the time it took to submit
842 the io. For sync io, the slat is really the completion
843 latency, since queue/complete is one operation there. This
844 value can be in miliseconds or microseconds, fio will choose
845 the most appropriate base and print that. In the example
846 above, miliseconds is the best scale.
847 clat= Completion latency. Same names as slat, this denotes the
848 time from submission to completion of the io pieces. For
849 sync io, clat will usually be equal (or very close) to 0,
850 as the time from submit to complete is basically just
851 CPU time (io has already been done, see slat explanation).
852 bw= Bandwidth. Same names as the xlat stats, but also includes
853 an approximate percentage of total aggregate bandwidth
854 this thread received in this group. This last value is
855 only really useful if the threads in this group are on the
856 same disk, since they are then competing for disk access.
857 cpu= CPU usage. User and system time, along with the number
858 of context switches this thread went through, usage of
859 system and user time, and finally the number of major
860 and minor page faults.
861 IO depths= The distribution of io depths over the job life time. The
862 numbers are divided into powers of 2, so for example the
863 16= entries includes depths up to that value but higher
864 than the previous entry. In other words, it covers the
866 IO submit= How many pieces of IO were submitting in a single submit
867 call. Each entry denotes that amount and below, until
868 the previous entry - eg, 8=100% mean that we submitted
869 anywhere in between 5-8 ios per submit call.
870 IO complete= Like the above submit number, but for completions instead.
871 IO issued= The number of read/write requests issued, and how many
873 IO latencies= The distribution of IO completion latencies. This is the
874 time from when IO leaves fio and when it gets completed.
875 The numbers follow the same pattern as the IO depths,
876 meaning that 2=1.6% means that 1.6% of the IO completed
877 within 2 msecs, 20=12.8% means that 12.8% of the IO
878 took more than 10 msecs, but less than (or equal to) 20 msecs.
880 After each client has been listed, the group statistics are printed. They
883 Run status group 0 (all jobs):
884 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
885 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
887 For each data direction, it prints:
889 io= Number of megabytes io performed.
890 aggrb= Aggregate bandwidth of threads in this group.
891 minb= The minimum average bandwidth a thread saw.
892 maxb= The maximum average bandwidth a thread saw.
893 mint= The smallest runtime of the threads in that group.
894 maxt= The longest runtime of the threads in that group.
896 And finally, the disk statistics are printed. They will look like this:
898 Disk stats (read/write):
899 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
901 Each value is printed for both reads and writes, with reads first. The
904 ios= Number of ios performed by all groups.
905 merge= Number of merges io the io scheduler.
906 ticks= Number of ticks we kept the disk busy.
907 io_queue= Total time spent in the disk queue.
908 util= The disk utilization. A value of 100% means we kept the disk
909 busy constantly, 50% would be a disk idling half of the time.
915 For scripted usage where you typically want to generate tables or graphs
916 of the results, fio can output the results in a semicolon separated format.
917 The format is one long line of values, such as:
919 client1;0;0;1906777;1090804;1790;0;0;0.000000;0.000000;0;0;0.000000;0.000000;929380;1152890;25.510151%;1078276.333333;128948.113404;0;0;0;0;0;0.000000;0.000000;0;0;0.000000;0.000000;0;0;0.000000%;0.000000;0.000000;100.000000%;0.000000%;324;100.0%;0.0%;0.0%;0.0%;0.0%;0.0%;0.0%;100.0%;0.0%;0.0%;0.0%;0.0%;0.0%
920 ;0.0%;0.0%;0.0%;0.0%;0.0%
922 Split up, the format is as follows:
924 jobname, groupid, error
926 KiB IO, bandwidth (KiB/sec), runtime (msec)
927 Submission latency: min, max, mean, deviation
928 Completion latency: min, max, mean, deviation
929 Bw: min, max, aggregate percentage of total, mean, deviation
931 KiB IO, bandwidth (KiB/sec), runtime (msec)
932 Submission latency: min, max, mean, deviation
933 Completion latency: min, max, mean, deviation
934 Bw: min, max, aggregate percentage of total, mean, deviation
935 CPU usage: user, system, context switches, major faults, minor faults
936 IO depths: <=1, 2, 4, 8, 16, 32, >=64
937 IO latencies: <=2, 4, 10, 20, 50, 100, 250, 500, 750, 1000, >=2000
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