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 size=x Set file size to x bytes (x string can include k/m/g)
45 ioengine=x 'x' may be: aio/libaio/linuxaio for Linux aio,
46 posixaio for POSIX aio, sync for regular read/write io,
47 mmap for mmap'ed io, splice for using splice/vmsplice,
48 or sgio for direct SG_IO io. The latter only works on
49 Linux on SCSI (or SCSI-like devices, such as
50 usb-storage or sata/libata driven) devices.
51 iodepth=x For async io, allow 'x' ios in flight
52 overwrite=x If 'x', layout a write file first.
53 prio=x Run io at prio X, 0-7 is the kernel allowed range
54 prioclass=x Run io at prio class X
55 bs=x Use 'x' for thread blocksize. May include k/m postfix.
56 bsrange=x-y Mix thread block sizes randomly between x and y. May
57 also include k/m postfix.
58 direct=x 1 for direct IO, 0 for buffered IO
59 thinktime=x "Think" x usec after each io
60 rate=x Throttle rate to x KiB/sec
61 ratemin=x Quit if rate of x KiB/sec can't be met
62 ratecycle=x ratemin averaged over x msecs
63 cpumask=x Only allow job to run on CPUs defined by mask.
64 fsync=x If writing, fsync after every x blocks have been written
65 startdelay=x Start this thread x seconds after startup
66 timeout=x Terminate x seconds after startup
67 offset=x Start io at offset x (x string can include k/m/g)
68 invalidate=x Invalidate page cache for file prior to doing io
69 sync=x Use sync writes if x and writing
70 mem=x If x == malloc, use malloc for buffers. If x == shm,
71 use shm for buffers. If x == mmap, use anon mmap.
72 exitall When one thread quits, terminate the others
73 bwavgtime=x Average bandwidth stats over an x msec window.
74 create_serialize=x If 'x', serialize file creation.
75 create_fsync=x If 'x', run fsync() after file creation.
76 end_fsync=x If 'x', run fsync() after end-of-job.
77 loops=x Run the job 'x' number of times.
78 verify=x If 'x' == md5, use md5 for verifies. If 'x' == crc32,
79 use crc32 for verifies. md5 is 'safer', but crc32 is
80 a lot faster. Only makes sense for writing to a file.
81 stonewall Wait for preceeding jobs to end before running.
82 numjobs=x Create 'x' similar entries for this job
83 thread Use pthreads instead of forked jobs
85 zoneskip=y Zone options must be paired. If given, the job
86 will skip y bytes for every x read/written. This
87 can be used to gauge hard drive speed over the entire
88 platter, without reading everything. Both x/y can
90 iolog=x Open and read io pattern from file 'x'. The file must
91 contain one io action per line in the following format:
93 where with rw=0/1 for read/write, and the offset
94 and length entries being in bytes.
97 Examples using a job file
98 -------------------------
100 A sample job file doing the same as above would look like this:
110 And fio would be invoked as:
112 $ fio -o1 -s -f file_with_above
114 The second example would look like this:
129 And fio would be invoked as:
131 $ fio -o0 -s -b4096 -f file_with_above
133 'global' is a reserved keyword. When used as the filename, it sets the
134 default options for the threads following that section. It is possible
135 to have more than one global section in the file, as it only affects
138 Also see the examples/ dir for sample job files.
141 Interpreting the output
142 -----------------------
144 fio spits out a lot of output. While running, fio will display the
145 status of the jobs created. An example of that would be:
147 Threads now running: 2 : [ww] [5.73% done]
149 The characters inside the square brackets denote the current status of
150 each thread. The possible values (in typical life cycle order) are:
154 P Thread setup, but not started.
155 C Thread created and running, but not doing anything yet
156 R Running, doing sequential reads.
157 r Running, doing random reads.
158 W Running, doing sequential writes.
159 w Running, doing random writes.
160 V Running, doing verification of written data.
161 E Thread exited, not reaped by main thread yet.
164 The other values are fairly self explanatory - number of thread currently
165 running and doing io, and the estimated completion percentage.
167 When fio is done (or interrupted by ctrl-c), it will show the data for
168 each thread, group of threads, and disks in that order. For each data
169 direction, the output looks like:
171 Client1 (g=0): err= 0:
172 write: io= 32MiB, bw= 666KiB/s, runt= 50320msec
173 slat (msec): min= 0, max= 136, avg= 0.03, dev= 1.92
174 clat (msec): min= 0, max= 631, avg=48.50, dev=86.82
175 bw (KiB/s) : min= 0, max= 1196, per=51.00%, avg=664.02, dev=681.68
176 cpu : usr=1.49%, sys=0.25%, ctx=7969
178 The client number is printed, along with the group id and error of that
179 thread. Below is the io statistics, here for writes. In the order listed,
182 io= Number of megabytes io performed
183 bw= Average bandwidth rate
184 runt= The runtime of that thread
185 slat= Submission latency (avg being the average, dev being the
186 standard deviation). This is the time it took to submit
187 the io. For sync io, the slat is really the completion
188 latency, since queue/complete is one operation there.
189 clat= Completion latency. Same names as slat, this denotes the
190 time from submission to completion of the io pieces. For
191 sync io, clat will usually be equal (or very close) to 0,
192 as the time from submit to complete is basically just
193 CPU time (io has already been done, see slat explanation).
194 bw= Bandwidth. Same names as the xlat stats, but also includes
195 an approximate percentage of total aggregate bandwidth
196 this thread received in this group. This last value is
197 only really useful if the threads in this group are on the
198 same disk, since they are then competing for disk access.
199 cpu= CPU usage. User and system time, along with the number
200 of context switches this thread went through.
202 After each client has been listed, the group statistics are printed. They
205 Run status group 0 (all jobs):
206 READ: io=64MiB, aggrb=22178, minb=11355, maxb=11814, mint=2840msec, maxt=2955msec
207 WRITE: io=64MiB, aggrb=1302, minb=666, maxb=669, mint=50093msec, maxt=50320msec
209 For each data direction, it prints:
211 io= Number of megabytes io performed.
212 aggrb= Aggregate bandwidth of threads in this group.
213 minb= The minimum average bandwidth a thread saw.
214 maxb= The maximum average bandwidth a thread saw.
215 mint= The minimum runtime of a thread.
216 maxt= The maximum runtime of a thread.
218 And finally, the disk statistics are printed. They will look like this:
220 Disk stats (read/write):
221 sda: ios=16398/16511, merge=30/162, ticks=6853/819634, in_queue=826487, util=100.00%
223 Each value is printed for both reads and writes, with reads first. The
226 ios= Number of ios performed by all groups.
227 merge= Number of merges io the io scheduler.
228 ticks= Number of ticks we kept the disk busy.
229 io_queue= Total time spent in the disk queue.
230 util= The disk utilization. A value of 100% means we kept the disk
231 busy constantly, 50% would be a disk idling half of the time.