On Mon, Jan 04, 2010 at 06:54:17AM -0800, Jack Z wrote: > Hi all, > > 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. > , in which /dev/sdb is the iSCSI device. I also measured TCP > throughput using iperf with the default setup except "-n 1024M". And I > got the following data on iSCSI throughput and TCP throughput v.s. rtt > > rtt (ms) iSCSI throughput by dd (MB/s) TCP throughput by > iperf (Mbit/s) > 0.2 11.3 > 94.3 > 4 11.1 > 94.3 > 8 10.2 > 94.3 > 12 8.6 > 94.2 > 16 7.2 > 94.2 > 20 6.0 > 94.1 > > local disk throughput by dd was 26.7 MB/s. > > As shown in the table above, iSCSI throughput declined rapidly with > rtt increased from 0.2ms to 20ms. TCP throughput, however, only > dropped less than 1 percent. > 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. -- Pasi -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to open-is...@googlegroups.com. To unsubscribe from this group, send email to open-iscsi+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/open-iscsi?hl=en.