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

[Tim Post <tim.post@xxxxxxxxxxxxxxx>]

On Wed, 2006-10-18 at 00:32 +0200, Kenneth Kalmer wrote:
> Greeting list

Hello :)

> 
> 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.

Be careful what you ask for :P

> 
> 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"
> 

I'm going to ask the same 'why not use lvm' question here, and toss in
the idea of replacing NFS with AoE. LVM read only snapshots are rather
safe.

If you don't want to use LVM, setup ocfs2 and join dom-0 and the nas to
the same cluster.

Format a big partition on the nas (ocfs2) , create your loops there as
you would normally with ext3 file systems. Export it as 0 0 and all of
your xen nodes (dom-0) have access. 

Mount the big partition via AoE on dom-0, get the loop and boot it, then
use the sysrq method to sync and rdiff to backup as you said. Doing
this, however is only really basically emulating what a lvm/clvm
snapshot would do. However I admire your drive toward simplicity, I have
no love for LVM either, but realize its use in this type of setting,
despite bad past experiences. 

This would of course work with NFS, but nfs will be a bottleneck. 

> 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
> xmlvalidation.com.

Again, use AoE. Faster, easier ..

> 
> 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.

I think with a better network fs and medium (aoe and ocfs2) you'd get
the performance increase you want and simplify things, while removing
the hassle of nfs. Migration would also be very easy. Remember, loops
can be exported as block devices via AoE too :) I'm still going to
officially recommend LVM + AoE as it solves all of your problems, but
completely understand a reluctance to use it and the need for something
a little different.

> 
> Any feedback would be dually appreciated.
> 

Best,
-Tim


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