How to take periodic snapshots of VMs and efficiently transport them off-site

disaster-recoverykvm-virtualizationrsyncsnapshot

I'm running KVM on Debian Squeeze and have VMs ranging from Debian to Windows Server 2003 to XP and W7

My plan is to move these VMs to qcow2 and use libvirt's snapshot-create to take periodic snapshots and rsync to copy the images to a remote site. I am happy to lose the running state and all changes since the last snapshot – this is only part of the overall backup strategy.

Am I right to assume I need to take an underlying LVM snapshot and run rsync from that to avoid corruption?
Will rsync efficiently copy only the tail-end of the image file that has changed since the previous rsync?

Best Answer

LVM snapshot are required if you can't pause for a few minutes running VMs during the backup procedure. If isn't critical for your applications, for every VM, you can freeze it when the backup procedure starts, rsync its virtual disk where you like, and finally resume it.

Rsync is a great tool, but keep in consideration that keeping incremental backups is generally more "secure" than keeping a daily rsynced copy: I use a combo of a shell script to rsync disk images, and a centralized backuppc server that acquire incremental backups of VM files (internal, not the disk images).

Related Solutions

Linux – mount qcow2 snapshots

You should apply the snapshot and mount the image like always. It's better to create a snapshot right before applying if you want to turn back to the original disk contents before you do these operations. After you apply the snapshot you just mount the image with qemu-nbd as always:

# modprobe nbd max_part=8
$ qemu-img snapshot -c backup image.qcow2
$ qemu-img snapshot -a old_snapshot image.qcow2
$ qemu-nbd --connect=/dev/nbd0 image.qcow2
# mount /dev/nbd0p1 /mnt

You might want to save snapshot separately and mount it as another disk drive. For this you should use convert comand for qemu-img.

$ qemu-img convert -s old_snapshot image.qcow2 old_snapshot.qcow2
$ qemu-nbd --connect=/dev/nbd0 old_snapshot.qcow2
# mount /dev/nbd0p1 /mnt

See man qemu-img(1) and qemu-nbd(1) for more details.

Linux – LVM-snapshot based KVM VMs

LVM snapshots currently suffer horrible performance when you try to create multiple snapshots of the same origin at once, and you must reserve space for each snapshot separately, so this is not a good idea. You would be much better off using qcow2 images instead of raw lvm volumes, as they do have good snapshot support, and you can set up a read only base image for multiple read/write images for different VMs to use as a shared starting point.

Best Answer

Related Solutions

Linux – mount qcow2 snapshots

Linux – LVM-snapshot based KVM VMs

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