[Xen-users] Backup running domUs (was iSCSI Volumes and Xen)

["Matthew Law" <matt@xxxxxxxxxxxxxxxxxx>]

On Thu, January 14, 2010 6:33 pm, Nick Couchman wrote:
> Backups and Snapshots have different purposes and aren't mutually
> exclusive.  I use both - backups are stored on separate media so that if I
> lose my entire disk array I have a copy of the data, snapshots allow for
> quick recovery in the case of an operator error, application bug, guarding
> against rogue updates, etc.  ZFS's ability to send/receive may mitigate
> the separate storage issue usually associated with snapshots, as it will
> allow you to snapshot and then send that data to another array.  Also,
> even with conventional backups, you still need a way to halt transactions
> on your applications for long enough to be able to get a clean copy of the
> data.  The problem is the same for both snapshots and backups - in both
> cases, you either need to make sure that the application is capable of
> recovering from an unclean shutdown or that you're flushing everything to
> disk before you suck the data off.

How do the so-called 'bare metal recovery' solutions do it on real running
boxes? - I've always assumed they had some hook into the kernel to force a
flush of the IO or maybe some scripts for installed daemons.

I suppose the only way one can guarantee the snapshot is consistent (yes,
I know its still only a snapshot) is to actually shutdown the domU
properly and snapshot the lvm before restarting it?

Interesting issues.  This must be something that people run into a lot. 
Is there something being worked on to do this through the hypervisor
somehow?  Do the likes of kvm and vmware have the same problem?

Thanks,

Matt


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