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Re: XFS and XEN

To: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Subject: Re: XFS and XEN
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 19 Feb 2009 14:35:52 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <93532303b1bb223328b2aaf712e0022f@xxxxxxxxxxxxxx>
References: <20090217091124.GA7118@xxxxxxxxxxxxx> <93532303b1bb223328b2aaf712e0022f@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Tue, Feb 17, 2009 at 03:00:39PM +0100, Michael Monnerie wrote:
> "Christoph Hellwig" <hch@xxxxxxxxxxxxx> schrieb:
> > I'm not even sure the Xen driver implements barriers.  I haven't done
> > much with Xen, but with the default kvm/qemu config I can completely
> > wreck ext3 and XFS filesystems.  If using these virtualization solutions
> > make sure you do not cache the virtual block device in the host
> > pagecache, and that in doubt the write cache of the disk is turned off
> > as barriers most likely won't work through the virtualization stack.
> How can I do that?

Barriers are disabled using hdparm.  To make sure qemu/kvm doesn't
cache your image file specify cache=off on the command line specifying
that virtual disk.

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