On Sep 15, 2009, at 9:01 PM, Majed B. wrote:
I think someone mentioned in the mailing list that the Linux kernel does sort commands before sending them to the disks, so if the disk tries to sort, and its algorithm isn't that good, the performance drops and hence disabling them is a good idea. I believe it's also mentioned in here: http://linux-raid.osdl.org/index.php/Performance
It depends on the elevator in use. And regardless, I have yet to see a raid5 array ever perform better with queueing turned off instead of on. Although, in many cases, very large queue depths don't help much. Testing I've done showed that only a 4 to 8 queue depth is sufficient to get 95% or better of the performance benefit of queueing.
-- Doug Ledford <dledford@xxxxxxxxxx> GPG KeyID: CFBFF194 http://people.redhat.com/dledford InfiniBand Specific RPMS http://people.redhat.com/dledford/Infiniband
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