I think what you’re looking for is LVM snapshots. The whole purpose of taking VM snapshots is to have a consistent image of the machine as a whole. There’s lots of articles out there on LVM snapshots, here’s one.

   http://www.tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html

From: libvirt-users-bounces@redhat.com [mailto:libvirt-users-bounces@redhat.com] On Behalf Of cmcc.dylan
Sent: Saturday, June 22, 2013 11:13 AM
To: libvirt-users@redhat.com
Subject: [libvirt-users] snapshot-create-as for a single disk not all disks

Hi everyone!

   Is there any way to create snaphot for a single disk of a virtual machine. As I konw, "virsh snapshot-create-as domain_name  snapshot_name --disk-only" traverses all block devices to create snapshot. However I don't want to create snapshot except for root partition.

  The version of qemu and libvirt I used is as follows:

                qemu-1.4.2 and libvrit-0.10.2

  I meet an error when I delete the snapshot which is created by "snapshot-create-as" command. whether or not qemu(1.4.2) and libvirt(0.10.2) don't support the function currently.

   Look forward to your help!