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



Jens Axboe wrote:
> On Mon, Feb 16 2004, Miquel van Smoorenburg wrote:
>
>>Hello,
>>
>>	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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