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Re: RE: [Xen-devel] poor domU VBD performance.

To: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>
Subject: Re: RE: [Xen-devel] poor domU VBD performance.
From: Kurt Garloff <garloff@xxxxxxx>
Date: Tue, 29 Mar 2005 15:34:08 +0200
Cc: Peter Bier <peter_bier@xxxxxx>, Andrew Theurer <habanero@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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On Mon, Mar 28, 2005 at 09:14:10PM +0100, Ian Pratt wrote:
> > Is the second disk exactly the same as the first one?  I'll 
> > try an IO test 
> > here on the same disk array with dom0 and domU and see what I get.
> I've reproduced the problem and its a real issue. 
> It only affects reads, and is almost certainly down to how the blkback
> driver passes requests down to the actual device.

Two points to look at:
* Block size (filesystems set this to 4k normally, default it 1k)
* Read ahead (you need to do it, otherwise you end up doing tiny
  requests). You can tune it in sysfs.

Kurt Garloff, Director SUSE Labs, Novell Inc.

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