Messages in this thread | | | From | Ian Soboroff <> | Subject | Re: io performance... | Date | Fri, 20 Jan 2006 08:42:35 -0500 |
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Max Waterman <davidmaxwaterman+kernel@fastmail.co.uk> writes:
> Phillip Susi wrote: >> Right, the kernel does not know how many disks are in the array, so >> it can't automatically increase the readahead. I'd say increasing >> the readahead manually should solve your throughput issues. > > Any guesses for a good number? > > We're in RAID10 (2+2) at the moment on 2.6.8-smp. These are the block > numbers I'm getting using bonnie++ : > >[...] > We're still wondering why rd performance is so low - seems to be the > same as a single drive. RAID10 should be the same performance as RAID0 > over two drives, shouldn't it?
I think bonnie++ measures accesses to many small files (INN-like simulation) and database accesses. These are random accesses, which is the worst access pattern for RAID. Seek time in a RAID equals the longest of all the drives in the RAID, rather than the average. So bonnie++ is domninated by your seek time.
Ian
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