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Re: [Xen-users] Backup DomU volumes

To: Pavel Georgiev <pavel@xxxxxxxxxxxx>
Subject: Re: [Xen-users] Backup DomU volumes
From: Marc Patino Gómez <mpatino@xxxxxxxxxxxx>
Date: Tue, 02 Oct 2007 15:57:26 +0200
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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,


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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