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Date: Tue, 14 Oct 2008 09:32:54 -0500
From: Ryan Harper <ryanh@us.ibm.com>
Subject: Re: [Qemu-devel] Re: [RFC] Disk integrity in QEMU
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To: Kevin Wolf <kwolf@suse.de>
Cc: Chris Wright <chrisw@redhat.com>, Mark McLoughlin <markmc@redhat.com>, kvm-devel <kvm-devel@lists.sourceforge.net>, Laurent Vivier <Laurent.Vivier@bull.net>, qemu-devel@nongnu.org, Ryan Harper <ryanh@us.ibm.com>, Laurent Vivier <laurent@lvivier.info>

* Kevin Wolf <kwolf@suse.de> [2008-10-14 05:10]:
> Ryan Harper schrieb:
> > * Laurent Vivier <laurent@lvivier.info> [2008-10-13 13:52]:
> >> What file type do you use (qcow2, raw ?).
> > 
> > Raw.
> 
> I guess the image is preallocated? What about sparse files (or qcow2,
> anything that grows), do have numbers on those? In the past, I
> experienced O_DIRECT to be horribly slow on them.
> 
> Well, looking at your numbers, they _are_ quite bad, so maybe it
> actually was sparse. Then the preallocated case would be interesting.

It was pre-allocated.  I'm incliding to think there is an alignment or
some sort of bug/edge-case in the write path to the file on top of the
lvm volume considering I don't see such horrible performance against the
file in host via O_DIRECT.  I imagine until I figure out the issue,
sparse or preallocated will perform the same.

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com