Pasi Kärkkäinen wrote:
On Tue, Oct 02, 2007 at 08:57:28PM +0300, Pasi Kärkkäinen wrote:
On Tue, Oct 02, 2007 at 09:39:09AM -0400, Ross S. W. Walker wrote:
Simon Banton wrote:
At 12:30 +0200 2/10/07, matthias platzer wrote:
What I did to work around them was basically switching
to XFS for
everything except / (3ware say their cards are fast,
but only on
XFS) AND using very low nr_requests for every blockdev
on the 3ware
card.
Hi Matthias,
Thanks for this. In my CentOS 5 tests the nr_requests
turned out by
default to be 128, rather than the 8192 of CentOS 4.5.
I'll have a go
at reducing it still further.
Yes, the nr_requests should be a realistic reflection of what the card itself can handle. If too high you will see io_waits stack up high.
64 or 128 are good numbers, rarely have I seen a card
that can handle
a depth larger then 128 (some older scsi cards did 256 I think).
Hmm.. let's say you have a linux software md-raid array made of sata drives.. what kind of nr_request values you should use for
that for optimal
performance?
Or let's put it this way:
You have a md-raid array on dom0. What kind of nr_requests values should you use for normal 7200 rpm sata-ncq disks on intel ich8 (ncq) controller?
And then this md-array is seen as xvdb by domU.. what kind of nr_requests values should you use in domU?
io-scheduler/elevator should be deadline in domU I assume.. how about in dom0? deadline there too?
Arrr, where thou go thar be monsters...
You got me Pasi, with Xen as the workload it adds a whole new dimension.
Unless you have hardware RAID, stick to the default setting and when you see a bottleneck double check your hardware drivers and RAID config first and only twiddle the queue settings if everything else has been twiddled first.
-Ross
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