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SubjectRe: [Xen-devel] domU is causing misaligned disk writes
On Tue, Apr 20, 2010 at 10:54:42PM +0300, Pasi Kärkkäinen spake thusly:
> Please try with "bs=1024k" and maybe with "bs=64k" aswell.
>
> 4k blocksize transfer will always be slower in domU than in dom0
> since virtual disk abstraction makes some overhead, which is more
> visible with small blocksizes.

But overhead in domU wouldn't be causing all of these reads. I am
doing a test with bs=64k now:

Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz
avgqu-sz await svctm %util
sda 0.00 3258.20 964.00 54.00 3903.20 13652.80
34.49 2.75 2.71 0.68 68.88
sdb 0.00 3270.20 974.80 54.00 3940.80 13710.40
34.31 2.42 2.38 0.55 56.22

> So the speed is the same to the partitioned disk than to the raw disk?
> What disk backend are you using in dom0? phy:? tap:aio: ?

Yes.

I am using phy: disk backend. Should I be using something else?

--
Tracy Reed
http://tracyreed.org
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