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Re: [Xen-users] A simple backup

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Subject: Re: [Xen-users] A simple backup
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Fri, 9 May 2008 09:08:28 +0100
Cc: "Fajar A. Nugraha" <fajar@xxxxxxxxx>, Steve Spencer <sspencer@xxxxxxxx>
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> Some thoughts about your comment.
> In our environment, one of the requirements for the OS and applications
> is that it must be able to recover quickly and cleanly from a power
> failure. This is actually one of the reasons why we're starting to
> migrate some stuff to zfs : because, when used properly, it always
> guarantee filesystem consistency in the event of power failure.
> IMHO, even the best commercial SAN-based backup solution uses that
> assumption, so for practical purposes, atomic backup for domU's storage
> should be sufficient.
> > It would be nicer if you could somehow guarantee a
> > consistent filesystem state on your disk snapshot.  I've been looking
> > into how to do this and I believe it's quite possible to modify the code
> > to support this properly.
> It would be interesting if you can make it happen.

Some investigation prompted by observations by users on this mailing list 
revealed that LVM can notify a filesystem *within the same VM* that it's 
going to be snapshotted so that it can put itself into a consistent state.  
I'd just like to add the plumbing so that you can tell a filesystem in 
another VM "You're going to get snapshotted by dom0.  Make your filesystem 
consistent so the snapshot will be mountable."


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