[linux-lvm] Re: IO scheduler, queue depth, nr_requests

Kevin P. Fleming kpfleming at backtobasicsmgmt.com
Mon Feb 16 19:32:00 UTC 2004

Jens Axboe wrote:
 > On Mon, Feb 16 2004, Miquel van Smoorenburg wrote:
 >>	as you might have seen from the linux-kernel mailinglist
 >>I have been testing for months now with a fileserver set up to
 >>use XFS over LVM2 on a 3ware RAID5 controller.

I too have been fighting lower-than-expected performance with this 
identical combination, other than using a P4 2.8GHz instead of 3.0GHz, 
and 1GB RAM instead of 2GB. My 3ware 8506-8 has six Seagate Barracuda 
SATA drives behind it, which are very fast on their own :-) Try as I 
might, with the 2.6 kernel I have not been able to generate a bonnie++ 
or iozone run that provided performance better than a single disk, even 
with the 3ware card in JBOD, RAID-0 or RAID-1 mode. I had been 
conversing with 3ware about it, but to no real effect given than they 
don't support 2.6 yet.

 >>By fiddling about today I just found that changing
 >>/sys/block/sda/queue/nr_requests from 128 to something above
 >>the queue depth of the 3ware controller (256 doesn't work,
 >>384 and up do) also fixes the problem.

I will try this as well this evening and report my results.

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