Hello, While running iSCSI performance tests I noticed that the performance for certain block sizes deviated significantly (more than ten times) from the performance for other block sizes, both larger and smaller. This surprised me.
The test I ran was as follows: * A file of 1 GB residing on a tmpfs filesystem was exported via iSCSI target software. The test has been repeated with both SCST and STGT. * On the initiator system open-iscsi version 2.0.870 was used for performing reads and writes with dd via direct I/O. Read-ahead was set to zero. * Both systems were running kernel 2.6.29.1 in run level 3 (no X server) and the 1 GbE interfaces in the two systems were connected via a crossed cable. The MTU has been left to its default value, 1500 bytes. Netperf reported a throughput of 600 Mbit/s = 75 MB/s for the TCP/IP stream test on this setup. * 128 MB of data has been transferred during each test. * Each measurement has been repeated three times. * All caches were flushed before each test. * The ratio of standard deviation to average was 2% or lower for all measurements. * The measurement result are as follows (transfer speeds in MB/s): Block SCST STGT SCST STGT size writing writing reading reading ------ ------- ------- ------- ------- 64 MB 71.7 63.3 62.1 58.4 32 MB 71.9 63.4 61.7 58.1 16 MB 72.4 63.0 61.7 57.1 8 MB 72.7 63.3 61.7 56.9 4 MB 72.9 63.5 61.3 57.0 2 MB 72.8 59.5 60.3 56.9 1 MB 72.1 38.7 59.4 56.0 512 KB 67.3 21.4 58.0 54.4 256 KB 67.4 22.8 55.5 53.4 128 KB 60.9 22.6 53.3 51.7 64 KB 53.2 22.2 53.0 45.7 32 KB 48.9 21.6 40.0 40.0 16 KB 40.0 20.8 0.6 1.3 8 KB 20.0 19.9 19.9 20.0 4 KB 0.6 1.6 18.9 10.3 All results look normal to me, except the write throughput for a block size of 4 KB and the read throughput for a block size of 16 KB. Regarding CPU load: during the 4 KB write test, the CPU load was 0.9 on the initiator system and 0.1 on the target. Has anyone observed similar behavior before ? Bart. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to open-iscsi@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 -~----------~----~----~----~------~----~------~--~---
