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Re: [Xen-users] xen domU backups

To: Ferenc Wagner <wferi@xxxxxxx>
Subject: Re: [Xen-users] xen domU backups
From: John Haxby <john.haxby@xxxxxxxxxx>
Date: Wed, 15 Oct 2008 09:36:54 +0100
Cc: James Pifer <jep@xxxxxxxxxxxxxxxx>, Xen List <xen-users@xxxxxxxxxxxxxxxxxxx>
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Ferenc Wagner wrote:
James Pifer <jep@xxxxxxxxxxxxxxxx> writes:
Can you back up individual domUs (img files) while they are running?

Sure, but it will be an inconsistent backup.

"Inconsistent" is an understatement. The image file will be changing while you're backing up; you'll most likely end up with garbage in the parts of the guest file system that are even vaguely active while you're doing the back up.
Do you need to pause, make backup, un-pause?

That helps, but the backup will still contain dirty filesystems.

Sometimes it helps. If you do a save-backup-restore that helps even more, but be aware that if you ever restore and start the backup then it will continue doing what it did at the time of the backup. In fact, everything it had in progress at the time of the backup will be done again. At the "mostly harmless" end of the spectrum you'll get mail messages that were in a queue re-sent; at the other end of the spectrum ... Well, that depends on the applications.

You need the cooperation of those applications because you can't just blindly restore (and restart) the backed up domU image and hope that everything will be fine.

jch

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