Re: [Xen-users] Backup DomU volumes

[Marc Patino Gómez <mpatino@xxxxxxxxxxxx>]

Hi Pavel,

In my opinion, using LVM will help you. When you want  backup a running 
VM which his VBD is on a LVM volume you can make a snapshot, then mount 
the snapshot, after this, make the rsync and finally remove the snapshot.
Best regards,

Marc

Pavel Georgiev wrote:
> Hi List,
>
> I`m trying backup the volumes of VMs running on a xen server (3.1). I`ll 
> backup ext3 and reiserfs volumes. My goal is to backup them from Dom0 so that 
> I can avoid messing with DomU (adding scripts, cronjobs etc.). I have another 
> server running xen and I plan to keep exactly the same volumes on it so I can 
> start the VMs on this server in case my main server dies. 
>
> The way I see it, I`ll be mounting volumes on both servers and 
> doing 'rsync -avP' on the content (in order to avoid transferring already 
> existing file). The problem (maybe not a problem of xen, but I guess other 
> people have bumped into this) is how do I mount volumes without stopping the 
> VMs and without corrupting the data on the volumes. 
>
> When a volume is in use by a VM, it either has the "need_recovery" flag (ext3) 
> or cannot be mounted ro (reiserfs). I could remove the "need_recovery" flag 
> for ext3 volumes and mount them read-only, do the sync and then umount and 
> set the flag again. For reiserfs I could mount the volume read-write, remount 
> read-only and then do the sync. Are those two approaches safe? Is this going 
> to corrupt my volumes, after all I`ll do some writing (removing the flag for 
> ext3 and replaying the journal for reiserfs)?
> In general, what are my options if I want to copy the volumes to another 
> server (hopefully only the changed files) without stopping the VM. The rsync 
> does not have to be atomic, it is OK if DomU writes some data after I start 
> rsync.
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>   

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