Hi all,

I'm trying to use disktest to measure the performance of an iSCSI device but 
get extremely low throughput...

For example, I did

disktest -w -S0:1k -B 1024 /dev/sdb (/dev/sdb is the iSCSI device file, no 
partition or file system on it)

And the result was:
| 2010/01/05-02:58:26 | START | 27293 | v1.4.2 | /dev/sdb | Start
args: -w -S0:1024k -B 1024 -PA (-I b) (-N 8385867) (-K 4) (-c) (-p R)
(-L 1048577) (-D 0:100) (-t 0:2m) (-o 0)
| 2010/01/05-02:58:26 | INFO  | 27293 | v1.4.2 | /dev/sdb | Starting
pass
^C| 2010/01/05-03:00:58 | STAT  | 27293 | v1.4.2 | /dev/sdb | Total
bytes written in 85578 transfers: 87631872
| 2010/01/05-03:00:58 | STAT  | 27293 | v1.4.2 | /dev/sdb | Total
write throughput: 701055.0B/s (0.67MB/s), IOPS 684.6/s.
| 2010/01/05-03:00:58 | STAT  | 27293 | v1.4.2 | /dev/sdb | Total
Write Time: 125 seconds (0d0h2m5s)
| 2010/01/05-03:00:58 | STAT  | 27293 | v1.4.2 | /dev/sdb | Total
overall runtime: 152 seconds (0d0h2m32s)
| 2010/01/05-03:00:58 | END   | 27293 | v1.4.2 | /dev/sdb | User
Interrupt: Test Done (Passed)

As you can see, the throughput was only 0.67MB/s and only 85578
written in 87631872 transfers...
I also tweaked the options with "-p l" and/or "-I bd" (change seek
pattern to linear and/or speficy IO type as block and direct IO) but
no improvement happened...

I thought this low throughput could be caused by the link rate or disk 
problem, but dd ruled it out..

$ dd if=/dev/zero of=/dev/sdb bs=1024 count=1048576

The throughput is 7.2 MB/s.

There must be something I've done wrong with disktest... Could anyone maybe 
help me out here?

Thanks a lot!

jack 


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