>>> 10MB/sec does seem extremely poor. we've had read slowness when Linux block >>> device read-ahead was too small. Once properly configured, performance on >>> RAID-5 went from 150MB/sec to 500MB/sec, so the difference is dramatic. we >>> usually tune read-ahead (in Linux) buffers starting from 8MB to 32MB and >>> benchmark to see what works best. but your problem may be elsewhere... we've >>> never seen 10MB/sec... >> Have you got any pointers to where this can be adjusted? It seems >> (according to Google) there are countless methods and patches, most of >> which are for rather old kernel versions. > > man blockdev > blockdev --setra blocks /dev/sda > > It is part of util-linux-ng .
Thanks for the hint! This didn't make much difference for us, but that's probably because the array is RAID-1, so the array readahead already matched the individual disk readahead. Strangely enough increasing the readahead actually reduced the raw speed according to hdparm -t, which I wouldn't have thought would make a difference. What did make a huge difference is setting the NCQ depth to 1 (instead of the default 64) as Tim suggested. This brought raw read speed up from ~50MB/sec to almost 90MB/sec! Haven't yet had the machine under a large load so will be interesting to see how it copes, but now I really want the updated firmware from Dell! Cheers, Adam. _______________________________________________ Linux-PowerEdge mailing list [email protected] https://lists.us.dell.com/mailman/listinfo/linux-poweredge Please read the FAQ at http://lists.us.dell.com/faq
