On 06/15/2012 02:16 AM, Dave Chinner wrote:
Oh, I just noticed you are might be using CFQ (it's the default in dmesg). Don't - CFQ is highly unsuited for hardware RAID - it's hueristically tuned to work well on sngle SATA drives. Use deadline, or preferably for hardware RAID, noop.
I'm not sure if noop is really a good recommendation even with hw raid, especially if the the request queue size is high. This week I did some benchmarks with a high rq write size (triggered with sync_file_range(..., SYNC_FILE_RANGE_WRITE) ) and with noop concuring reads then almost entirely got stalled. With deadline read/write balance was much better, although writes still had been preferred (with sync_file_range() and without). I always thought deadline prefers reads and I hope I find some time later on to investigate further what was going on.
Test had been on a netapp E5400 hw raid, so rather high end hw raid. Cheers, Bernd _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
