Re: [Qemu-devel] Issue with snapshot outside qcow2 disk - qemu 0.14.0

[Jes Sorensen]

On 03/11/11 10:39, SAURAV LAHIRI wrote:
> Thank you Stefan, Jes. So it appears that snapshot_blkdev is the way
> to go for vm disk backup with running vms.
> 
> In regard to merging changes, assuming that we go snapshot_blkdev
> rightaway. Stefan's suggestion: "qemu-img commit" Jes's suggestion:
> "qemu-img convert"
> 
> Does qemu-img convert apply to running VM's. In that case it would
> appear to be the more practical approach(since vm shutdown would not
> be required).
> 
> Also incase If i have interpreted "qemu-img convert" incorrectly and
> does require a VM shutdown. Then when is expected time when the "live
> merge" will be available.

I believe commit only applies to images with internal files. If you use
convert then it doesn't modify the actual images, so lets say you have a
chain like this:

original->snapshotA->snapshotB

original and snapshotA are read-only when snapshotB is running.
Therefore you should be able to use convert to simply copy snapshotA
into a new image file snapshotX and save that for your backup. If you
later restore, you have a single image file you can boot from.

What you cannot do is to create the new snapshotX file and switch to it
as the backing file for snapshotB while you are up and running.

Cheers,
Jes