>What is the recurring performance problem you are seeing? Pretty much exactly the symptoms described in http://bugzilla.kernel.org/show_bug.cgi?id=7372 relating to read starvation under heavy write IO causing sluggish system response. I recently graphed the blocks in/blocks out from vmstat 1 for the same test using each of the four IO schedulers (see the PDF attached to the article below): http://community.novacaster.com/showarticle.pl?id=7492 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 & Despite appearances, interactive responsiveness subjectively felt better using deadline than cfq - but this is obviously an atypical workload and so now I'm focusing on finishing building the machine completely so I can try profiling the more typical patterns of activity that it'll experience when in use. I find myself wondering whether the fact that the array looks like a single SCSI disk to the OS means that cfq is able to perform better in terms of interleaving reads and writes to the card but that some side effect of its work is causing the responsiveness issue at the same time. Pure speculation on my part - this is way outside my experience. I'm also looking into trying an Areca card instead (avoiding LSI because they're cited as having the same issue in the bugzilla mentioned above). S.