I just did a talk at a small local conference (Infrastructure.Next, co-located with cfgmgmtcamp.eu) about Advanced Snapshots in libvirt and QEMU.
Slides are here, which contains URLs to more examples.
And, some more related notes here:
- An example with more details about live merging a disk image chain using libvirt..
- Live disk backup with libvirt’s
blockcommit - Live
blockcopywhile reusing existing destination. This allows you to (a) control what the backing file is, as long as the top of that backing file chain has identical guest contents to what the original chain sees as its backing file; (b) use the different file to be of different backing chain depth or even different format.
Kashyap Chamarthy 
Interesting. Your examples all use .qcow2 for the storage engine. Does this also work for .raw ?
Nice writeup. I see your examples all use .qcow2. Does this work with .raw also?
Raw files or LVM or direct block device can be used as the base image, but the overlays must be QCOW2.
always the problem with qemu/libvirt how-to’s … does it still apply to what is current or what I am running?
$ virsh -v
1.2.2
$ cat /etc/os-release
VERSION=”14.04.5 LTS, Trusty Tahr”
so, does the talk apply to those versions?