Fwd: Re: [Xen-users] xen storage options - plase advise

["J. Roeleveld" <joost@xxxxxxxxxxxx>]

On Thursday 04 March 2010 10:28:03 Matthew Law wrote:
> On Thu, March 4, 2010 12:38 am, James Pifer wrote:

<snipped>

> James,
> 
> I had similar questions a while ago and back then the consensus was that
> snapshotting a running domU does *not* provide a consistent backup.  This
> is especially the case with databases and applications which do not
> immediately flush writes to disk.  I believe XenServer may do a better
> job, but I am unsure on this.
> 
> Basically, the only way to do a proper backup is to properly shutdown the
> domU before taking the snapshot, thus ensuring there is no chance of
> losing data.  For some people not doing this is an acceptable risk and
> certainly better than no backup at all.

Another option, not sure how to do this with a MS Windows virtual machine, but 
that's for the MS Windows experts to work out, would be to do the following:
1) Stop service whose data you want to backup
2) Force the guest OS to flush data to disk
3) block-detach the partition (OPTIONAL)
4) create snapshot
5) block-attach the partition (OPTIONAL)
6) restart the service
7) backup the snapshot
8) delete the snapshot

detaching the partition is optional, if you can ensure the disk is in a 
consistent state for the backups.

I use Linux guests and force the "flush" by unmounting the partition. I then 
backup the snapshot by mounting it in the dom0 and running the backup on that.

--
Joost

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