Greetings,
running fio 1.41 randwrite, direct=1 tests on Ubuntu against an
iSCSI-connected disk reports IOPS figures higher than I would expect, so
now I am trying to understand what's going on. Any pointers or
enlightenment appreciated, e.g. where's a caching effect that I am
currently missing (and if there's one, how can I deactivate it)?
Setup:
* iSCSI storage exports a 10GB LUN which sits on a single 7.2K SATA disk [1]
Storage system write-cache is disabled (write-through)
* Client: Ubuntu 8.04 (kernel 2.6.24-28) w/ open-iscsi, 512MB RAM
* LUN mkfs.ext3'd and mounted on /mnt
* fio is configured to operate in O_DIRECT, O_SYNC mode
* Random write IOPS expected: <80
* Random write IOPS observed: ~300 (confirmed in multiple runs)
root@ubuntu-804-x64:~# df -h /mnt
Filesystem Size Used Avail Use% Mounted on
/dev/sdb1 9.7G 151M 9.1G 2% /mnt
root@ubuntu-804-x64:~# cat patterns.fio
[global]
size=9g
runtime=120
direct=1
sync=1
[mnt-randwrite]
directory=/mnt
rw=randwrite
root@ubuntu-804-x64:~# ./fio --section=mnt-randwrite patterns.fio
mnt-randwrite: (g=0): rw=randwrite, bs=4K-4K/4K-4K, ioengine=sync, iodepth=1
Starting 1 process
mnt-randwrite: Laying out IO file(s) (1 file(s) / 9216MB)
Jobs: 1 (f=1): [w] [100.0% done] [0K/1243K /s] [0/303 iops] [eta 00m:00s]
mnt-randwrite: (groupid=0, jobs=1): err= 0: pid=9398
write: io=126796KB, bw=1057KB/s, iops=264, runt=120010msec
clat (usec): min=486, max=332821, avg=3782.24, stdev=5744.57
bw (KB/s) : min= 187, max= 1641, per=100.27%, avg=1058.85, stdev=260.24
cpu : usr=0.02%, sys=0.19%, ctx=33866, majf=0, minf=241
IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
issued r/w: total=0/31699, short=0/0
lat (usec): 500=0.35%, 750=11.91%, 1000=1.97%
lat (msec): 2=4.43%, 4=66.01%, 10=9.15%, 20=4.74%, 50=1.36%
lat (msec): 100=0.06%, 250=0.02%, 500=0.01%
Run status group 0 (all jobs):
WRITE: io=126796KB, aggrb=1056KB/s, minb=1081KB/s, maxb=1081KB/s, mint=120010msec, maxt=120010msec
Disk stats (read/write):
sdb: ios=2091/31879, merge=0/33, ticks=30360/118040, in_queue=143320, util=99.30%
Unfortunately, this system as well as all the other Ubuntu systems which
I currently have access to are virtual machines, so I can't simply
compare the findings to a simple local disk.
Sebastian
[1] http://www.hitachigst.com/internal-drives/desktop/deskstar/deskstar-7k2000
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