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Re: [Xen-users] Backup; mount domU FS RO?

To: Ralf Folkerts <ralf.folkerts@xxxxxx>
Subject: Re: [Xen-users] Backup; mount domU FS RO?
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Sun, 18 Dec 2005 23:04:08 -0600
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Ralf Folkerts wrote:


I recently set-up a Xen Server that's hosting 3 Development Systems. It
works quite well, so it's time to put this into Production -- and to
perform regular Backups.

We use Bacula to Backup the dom0. My Idea was, to mount all domU
Filesystems Read-Only to some Directories and then back these up from
the Bacula-FD on the dom0.

I found some warnings that Filesystems may not be mounted RW by more
than one domain / system (makes sense when they don't "know" about each
other). However, are there any issues mounting a Filesystem Read-Only,
then have it being backed-up by Bacula and then unmount it?
When you mount a filesystem (even read-only) that's already mounted read-write, the filesystem will contain meta-data that says "I'm dirty and currently in use." Best case scenario it just refuses to mount. Worst case scenario fsck gets automagically invoked somehow in an attempt to repair the partition and you risk serious corruption.

Besides, you really don't want to back up a raw partition. There's no guarentee any application has the data in a consistent state. You really want to run a backup application with the domU. You could attach/detach a device to be the target of the backup from within dom0 at the appropriate scheduled time of course.


Anthony Liguori

Thanks for any hints in advance!


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