Hi Pasi, Thank you very much for your reply.
> > I was testing the performance of open-iscsi initiator with IET target > > over a 100Mbps Ethernet link with emulated rtt. What I did was to do > > raw disk sequential write by > > > $ dd if=/dev/zero of=/dev/sdb bs=1024 count=1048576 > > Did you also try with bigger block sizes? 1k blocks are pretty small. > > try bs=1024k to see if it makes a difference. I tried bs = 1024k and the throughput is improved, but not much... It goes from 7.2MB/s to 8.0MB/s at a rtt of 16ms. And again, over 90% of the TCP segments on the wire was only of 1448 bytes... > dd will use only one outstanding IO, so you have wait for rtt > milliseconds after every IO for the ack.. so that definitely slows you > down a lot when rtt gets bigger. > > Try using some benchmarking tool that can do multiple outstanding IOs.. > for example ltp disktest. > And I tried ltp disktest, too. But I'm not sure whether I used it right because the result was a little surprising... 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... There must be something I've done wrong... Could you maybe help me out here? Thanks a lot! jack
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