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xen-users
Re: [Xen-users] Backup domU
Kalil Costa - Brasilsite wrote:
I need to know which way to backup domU to restore these to another
server if i've problem with this machine.
There are many ways, all with their pros and cons.
One suggestion given here in the past was to send a signal (with an
xm command IIRC) to the guest (assuming guest with Xen support
included) to tell the guest to sync it's unwritten buffers to disk.
He then did a snapshot live via LVM.
Upside - no downtime on guest. Downside, your backups are of a
mounted filesystem with open files, partially written files,
whatever. Getting the guest to sync first reduces the impact so it's
not quite the same as the backup being analogous to what you'd find
on disk after pulling the power cord on a real machine.
The backup is also on the same disks as the live system.
You've just had a suggestion of stopping the guest before the LVM snapshot.
Upside - it's a 'clean' backup. Downsides - downtime for guest,
backup still on the same disks.
As a variation, you could pause the guest and snapshot the LVM
volumes **PLUS** save the guest saved state file. If you need to
restore then the guest would unpause in the same state as when it was
paused.
Personally I backup my guests as though they were real (non
virtualised) machines. There are many options for this - both free
and commercial.
At work I've setup a system where I have a VM dedicated just to
holding backups of the other machines - each of which uses rsync to
update a backup copy of itself on the backup server (the server runs
rsync in server mode). Thus I have a server holding a complete image
of each of my servers at the point they last backed up. Should a host
go down, I can move the guests to another host by creating volumes
for them and using rsync to pull their files back (mount the guest
filesystems on the host, use rsync on the host to pull the files,
unmount the filesystems and start the guest).
Of course, once you are using rsync, then it doesnt' matter whether
the destination is on the same host, another host in the same rack,
or half way round the world - as long as you have enough bandwidth.
On my backup machine I then copy the copies to create various levels
of historical backups. Again there are various ways of doing this, I
settled on StoreBackup which if you disable compression creates full
copies which you can just navigate into and use your normal
unix/linux tools to access files*. It saves space by hard-linking
identical files so it's fairly efficient.
You can do something similar with rsync and some scripting. Another
tool I looked at was rdiff-backup - but I didn't like the way you
can't thin out your backups, and they aren't readable without going
through the restore process.
* Just the other day I found this useful as I wanted to find out when
a DNS record had changed. I was able to grep
<something>/*/var/named/zones/<somezonefile> for the name in question
and find out that it changed about a month ago - yes no-one had
noticed a service was broken !
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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