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Re: [Xen-users] Consistent snapshots


Sorry to chime in so late.

Agreed with this.

But I've done a dump/restore on live and paused Xen domUs from my dom0 and haven't experience and issues (yet).

I am constantly doing dev work on the dump/restored image by copying it to my isolated box.

I also do an rsync from within that domU as well.

I had a weird/bad thing happen to me a while back on a non critical domU server.

i was only doing dump/restores and i rebooted my dom0 that the domU was on (yes, I manually shut down the domU) and when my dom0 came back up, my domUs image file (img) showed as an ACB archive file. Dude, i did the command; file name.img, and thats what came back.

My history of those dump/restored img files goes back as far as two weeks and they all showed as ACB archive files so the fu@#up happened before then and I didn't notice.

My setup was Centos 5.3 dom0 and a fully virtualized Ubuntu 7 domU. I set the disk to grow as needed.

Had I done rsyncs in addition to backing up the domU image, I would be fine.

Anyways, i'm still manipulating the img file in hopes of getting data from it.

Tyler has been EXTREMELY helpful on this but it doesn't look to be a simple task.

My advise is to use 2 diff backup methods;

1 - The img backup provides a fast and easy restore if needed.
2 - The rsync provides a more time consuming but non the less, a way to mitigate a failed primary backup.

- Brian

On Jun 25, 2009, at 3:23 AM, John Haxby wrote:

On 25/06/09 11:01, Gak wrote:
How do i create consistent snapshots of VM's from Dom0?. What are the backup methods or snapshot/snaprestore methods that are followed for Xen Virtual environments?.

Shut down the VM, take the snapshot.

Anything else requires serious cooperation from VM and, equally importantly, the applications running in it. Sometimes you can get away with suspending the guest and taking a snapshot of memory and disk at the same time -- that isn't very useful though because to recover, say, an individual file from the back up you have to restart the suspended copy. Even worse, if there are any in-flight transactions between the VM and other machines (virtual or otherwise) those will restart -- having your bank balance debited twice would be very annoying.

In the general case, you're better off running your backup within the VM. In special cases you can do something different -- for example, you might have a database that can get itself into a consistent state so you can take a snapshot of its file system on a suitable NAS or SAN.


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