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[Xen-users] Yet another backup proposal (file based vbd's & lvm)

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Yet another backup proposal (file based vbd's & lvm)
From: "Kenneth Kalmer" <kenneth.kalmer@xxxxxxxxx>
Date: Wed, 18 Oct 2006 00:32:52 +0200
Delivery-date: Tue, 17 Oct 2006 15:33:37 -0700
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Greeting list

This is yet another request for feedback on a proposed backup solution
for a xen environment, and I'll appreciate any all scrutiny of what I
want to attempt.

Key features of xen backups:
- Snapshot-like backups of domU's
- Avoiding LVM snapshots
- Near-zero downtime

First a brief overview of how we currently use Xen. We have a Linux
storage server attached to our network with two bonded gigabit
Ethernet cards. We have several dom0's running on this same network.
On the NAS we have a directory containing all our domU's as file-based
VBD's. Each dom0 runs their selected domU's from the NFS directly.
These domU's are basically just configured to offer a minimal amount
of services, and are really small. The only things of importance
inside them is the various configuration & user files for their
particular services. All the data they require to deliver their
services (WWW, POP, etc) also resides on the NAS under different
exports. The problem is that the NAS is performing very poorly with
this setup, and I intend to move the VM's from the NAS directly to the
hardware of their dom0, but before I take this leap of faith I need to
make sure I have a viable backup solution in place.

From what I've gathered in the list archives and google, LVM snapshots
are frowned upon, rdiff-backup seems to get decent remarks, and
dd-like backups are too slow and space consuming.

What I'd like to attempt to setup (based on the feedback I receive) is
the following.

1. Pause the domU using "xm pause"
2. Sync the domU using "xm sysrq"
3. Use rdiff-backup to make a local backup of the file VBD
4. Resume the domU using "xm unpause"

After this I can rsync the backup directory to another server while
the domU continues to run. This is based almost entirely on the
xen-server-tools backup script by Christian Wieke from

I can understand that the first backup will take a substantial amount
of time, afterwards it should take that long since the only things
that change inside our domU's are config files and log files,
everything else runs of the NAS.

We have all the domU's on the NFS to ease migration in case of
hardware failures, and I need to be able to restore a backup on
another machine within minutes of any critical failure. I believe the
above solution will work for file-based VBD's, albeit not the best or
fastest solution around.

Any feedback would be dually appreciated.


Kenneth Kalmer

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