4 fio is a tool that will spawn a number of thread doing a particular
5 type of io action as specified by the user. fio takes a number of
6 global parameters, each inherited by the thread unless otherwise
7 parameters given to them overriding that setting is given.
13 fio resides in a git repo, the canonical place is:
15 git://brick.kernel.dk/data/git/fio.git
17 Snapshots are frequently generated as well and they include the git
18 meta data as well. You can download them here:
20 http://brick.kernel.dk/snaps/
28 -b block size in KiB for each io
29 -t <sec> Runtime in seconds
30 -r For random io, sequence must be repeatable
31 -R <on> If one thread fails to meet rate, quit all
32 -o <on> Use direct IO is 1, buffered if 0
33 -l Generate per-job latency logs
34 -w Generate per-job bandwidth logs
35 -f <file> Read <file> for job descriptions
37 -v Print version information and exit
39 The <jobs> format is as follows:
41 directory=x Use 'x' as the top level directory for storing files
42 rw=x 'x' may be: read, randread, write, randwrite,
43 rw (read-write mix), randrw (read-write random mix)
44 rwmixcycle=x Base cycle for switching between read and write
46 rwmixread=x 'x' percentage of rw mix ios will be reads. If
47 rwmixwrite is also given, the last of the two will
48 be used if they don't add up to 100%.
49 rwmixwrite=x 'x' percentage of rw mix ios will be writes. See
51 size=x Set file size to x bytes (x string can include k/m/g)
52 ioengine=x 'x' may be: aio/libaio/linuxaio for Linux aio,
53 posixaio for POSIX aio, sync for regular read/write io,
54 mmap for mmap'ed io, splice for using splice/vmsplice,
55 or sgio for direct SG_IO io. The latter only works on
56 Linux on SCSI (or SCSI-like devices, such as
57 usb-storage or sata/libata driven) devices.
58 iodepth=x For async io, allow 'x' ios in flight
59 overwrite=x If 'x', layout a write file first.
60 prio=x Run io at prio X, 0-7 is the kernel allowed range
61 prioclass=x Run io at prio class X
62 bs=x Use 'x' for thread blocksize. May include k/m postfix.
63 bsrange=x-y Mix thread block sizes randomly between x and y. May
64 also include k/m postfix.
65 direct=x 1 for direct IO, 0 for buffered IO
66 thinktime=x "Think" x usec after each io
67 rate=x Throttle rate to x KiB/sec
68 ratemin=x Quit if rate of x KiB/sec can't be met
69 ratecycle=x ratemin averaged over x msecs
70 cpumask=x Only allow job to run on CPUs defined by mask.
71 fsync=x If writing, fsync after every x blocks have been written
72 startdelay=x Start this thread x seconds after startup
73 timeout=x Terminate x seconds after startup
74 offset=x Start io at offset x (x string can include k/m/g)
75 invalidate=x Invalidate page cache for file prior to doing io
76 sync=x Use sync writes if x and writing
77 mem=x If x == malloc, use malloc for buffers. If x == shm,
78 use shm for buffers. If x == mmap, use anon mmap.
79 exitall When one thread quits, terminate the others
80 bwavgtime=x Average bandwidth stats over an x msec window.
81 create_serialize=x If 'x', serialize file creation.
82 create_fsync=x If 'x', run fsync() after file creation.
83 end_fsync=x If 'x', run fsync() after end-of-job.
84 loops=x Run the job 'x' number of times.
85 verify=x If 'x' == md5, use md5 for verifies. If 'x' == crc32,
86 use crc32 for verifies. md5 is 'safer', but crc32 is
87 a lot faster. Only makes sense for writing to a file.
88 stonewall Wait for preceeding jobs to end before running.
89 numjobs=x Create 'x' similar entries for this job
90 thread Use pthreads instead of forked jobs
92 zoneskip=y Zone options must be paired. If given, the job
93 will skip y bytes for every x read/written. This
94 can be used to gauge hard drive speed over the entire
95 platter, without reading everything. Both x/y can
97 iolog=x Open and read io pattern from file 'x'. The file must
98 contain one io action per line in the following format:
100 where with rw=0/1 for read/write, and the offset
101 and length entries being in bytes.
102 lockmem=x Lock down x amount of memory on the machine, to
103 simulate a machine with less memory available. x can
104 include k/m/g suffix.
106 Examples using a job file
107 -------------------------
109 A sample job file doing the same as above would look like this:
119 And fio would be invoked as:
121 $ fio -o1 -s -f file_with_above
123 The second example would look like this:
138 And fio would be invoked as:
140 $ fio -o0 -s -b4096 -f file_with_above
142 'global' is a reserved keyword. When used as the filename, it sets the
143 default options for the threads following that section. It is possible
144 to have more than one global section in the file, as it only affects
147 Also see the examples/ dir for sample job files.
150 Interpreting the output
151 -----------------------
153 fio spits out a lot of output. While running, fio will display the
154 status of the jobs created. An example of that would be:
156 Threads now running: 2 : [ww] [5.73% done]
158 The characters inside the square brackets denote the current status of
159 each thread. The possible values (in typical life cycle order) are:
163 P Thread setup, but not started.
164 C Thread created and running, but not doing anything yet
165 R Running, doing sequential reads.
166 r Running, doing random reads.
167 W Running, doing sequential writes.
168 w Running, doing random writes.
169 V Running, doing verification of written data.
170 E Thread exited, not reaped by main thread yet.
173 The other values are fairly self explanatory - number of thread currently
174 running and doing io, and the estimated completion percentage.
176 When fio is done (or interrupted by ctrl-c), it will show the data for
177 each thread, group of threads, and disks in that order. For each data
178 direction, the output looks like:
180 Client1 (g=0): err= 0:
181 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
182 slat (msec): min= 0, max= 136, avg= 0.03, dev= 1.92
183 clat (msec): min= 0, max= 631, avg=48.50, dev=86.82
184 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, dev=681.68
185 cpu : usr=1.49%, sys=0.25%, ctx=7969
187 The client number is printed, along with the group id and error of that
188 thread. Below is the io statistics, here for writes. In the order listed,
191 io= Number of megabytes io performed
192 bw= Average bandwidth rate
193 runt= The runtime of that thread
194 slat= Submission latency (avg being the average, dev being the
195 standard deviation). This is the time it took to submit
196 the io. For sync io, the slat is really the completion
197 latency, since queue/complete is one operation there.
198 clat= Completion latency. Same names as slat, this denotes the
199 time from submission to completion of the io pieces. For
200 sync io, clat will usually be equal (or very close) to 0,
201 as the time from submit to complete is basically just
202 CPU time (io has already been done, see slat explanation).
203 bw= Bandwidth. Same names as the xlat stats, but also includes
204 an approximate percentage of total aggregate bandwidth
205 this thread received in this group. This last value is
206 only really useful if the threads in this group are on the
207 same disk, since they are then competing for disk access.
208 cpu= CPU usage. User and system time, along with the number
209 of context switches this thread went through.
211 After each client has been listed, the group statistics are printed. They
214 Run status group 0 (all jobs):
215 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
216 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
218 For each data direction, it prints:
220 io= Number of megabytes io performed.
221 aggrb= Aggregate bandwidth of threads in this group.
222 minb= The minimum average bandwidth a thread saw.
223 maxb= The maximum average bandwidth a thread saw.
224 mint= The minimum runtime of a thread.
225 maxt= The maximum runtime of a thread.
227 And finally, the disk statistics are printed. They will look like this:
229 Disk stats (read/write):
230 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
232 Each value is printed for both reads and writes, with reads first. The
235 ios= Number of ios performed by all groups.
236 merge= Number of merges io the io scheduler.
237 ticks= Number of ticks we kept the disk busy.
238 io_queue= Total time spent in the disk queue.
239 util= The disk utilization. A value of 100% means we kept the disk
240 busy constantly, 50% would be a disk idling half of the time.