Re: [Xen-users] Consistent snapshots

[Brian Krusic <brian@xxxxxxxxxx>]

Hi,

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.
> jch
>
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