Re: 3Ware SATA Raid 9550SX Performance - scheduler comparison
by Simon at 17:03 02/10/07 (Forum::Technical Advice::General)
Attached PDFs show graphs of vmstat -n 1 recorded 'bi' and 'bo' data for the same test using different io schedulers under a fresh install of CentOS 5 with the built-in 3w-9xxx driver.

The test was:

dd if=/dev/sda of=/dev/null bs=1M count=4096 &; sleep 5; dd if=/dev/zero of=./4G bs=1M count=4096 &

Twin Opteron 2.4GHz, 4GB RAM, 3ware 9550SX RAID 1, built-in driver, nr_requests 128 (default), ext3 on LVM (default), data=default (as opposed to 'writeback' or other non-default tweaks). All other filesystem/kernel param settings also at default for the CentOS 5 install - only the io scheduler is being changed.

Also tested the 3ware src-compiled driver and saw identical results.

Edit: Redid tests with 4k blocksize and count 1048576 - very similar graphs.

PDF file (30 K) CentOS 5 io scheduler comparisons 1M block size
PDF file (30 K) Same tests but with 1048576 blocks of 4k size instead
JPG image (186 K) Comparison of 1M v 4k bs side by side
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