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Re: puzzling error: XenServer, LVM and XFS

To: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Subject: Re: puzzling error: XenServer, LVM and XFS
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 27 May 2010 07:51:53 -0400
Cc: xfs@xxxxxxxxxxx
In-reply-to: <201005270857.39048@xxxxxx>
References: <201005270857.39048@xxxxxx>
User-agent: Mutt/1.5.19 (2009-01-05)
On Thu, May 27, 2010 at 08:57:38AM +0200, Michael Monnerie wrote:
> May 27 08:32:11 zdb13 kernel: [  738.046895] end_request: I/O error, dev 
> xvdc, sector 0
> This only happens after XFS is mounted from the LVM volume. On another 
> machine where active I/O is happening, I get tons of these errors every 
> some seconds.

This looks like the Xen block device code is buggy and doesn't handle
the I/O pattern XFS throws at it.  A sector 0 error during mount usually
is the superblock barrier test write.  To verify that assumptions
try mounting the XFS filesystems with -o nobarrier and see if it goes
away.  Note that this is only for testing, and I would _not_ recommend
it for production use.  If it makes the error go away please file
a bug with the Xen guys to fix their barrier support by either
implementing it properly or not advertizing it.

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