From: Norbert Paschedag (noe_at_physik.unizh.ch)
Date: Mon Aug 13 2007 - 12:40:54 CEST
Date: Mon, 13 Aug 2007 12:40:54 +0200 (CEST) From: Norbert Paschedag <noe@physik.unizh.ch> Message-ID: <Pine.LNX.4.64.0708131207280.5471@hesse.math.tu-berlin.de> Subject: Re: [suse-sles-e] sles10sp1: xfs + lvm + snapshot = Input/output error
On Fri, 10 Aug 2007, Dr J Pelan wrote:
>
> On Wed, 8 Aug 2007, Norbert Paschedag wrote:
>
> > we just stumbled over a problem with lvm snapshotting of xfs
> > filesystems. Just creating a snapshot of a _mounted_ volume and then
> > accessing the original filesystem creates an I/O error. Has anyone else
> > seen this and knows a way to prevent this ?
>
> Good catch. I'd just like to confirm that this problem is reproducable
> here on a fully patched SLES10+SP1 test system (x86_64). It seems that
> after a remount subsequent snapshots do not cause problems so there is a
> workaround of sorts, but I would not deem this acceptable for production.
My colleague investigated further and found that the error appears only
on xfs filesystems that have barriers enabled.
In the presence of a snapshot, mounting the original filesystem will
disable barriers (also in ext3). This explains why the error goes away
after doing the recommended umount/mount.
File systems can be mounted without barriers using the undocumented
mount -o nobarrier <dev> <mntpt>
Can anyone with more knowledge of the SLES kernel explain what xfs patches
made it into the kernel since SLES10 ?
Officially (I think) barriers are on by default only in kernel >= 2.6.17.
Norbert
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