Re: [Qemu-devel] Derivative snapshots or snapshots for versioning

[Mike Young]

Thanks Stefan!

On 5/25/11 1:21 AM, "Stefan Hajnoczi" <address@hidden> wrote:

>On Tue, May 24, 2011 at 5:14 PM, Mike Young <address@hidden>
>wrote:
>> I'm trying to see if I can I do a derivative snapshot as a means of
>> versioning. I wish to do this vs dd or cp as it's much faster. I do not
>> intend to apply a snapshot back to an original volume.
>> So, let's say I have original_volume.img and I create a snapshot using
>>the
>> ­b option: "qemu-img create ­f qcow2 ­b original_volume.img
>>snapshot1.img",
>
>I would not call the new file "snapshot1.img" since the frozen disk
>image should be original_volume.img.  You can write to snapshot1.img
>but it is not safe to original_volume.img because snapshot1.img will
>then become inconsistent (you've changed the blocks that it was based
>on).
>
>> but now I wish to create a snapshot2 from snapshot1.img. Is there a way
>>to
>> do this?
>
>qemu-img create -f qcow2 -b snapshot1.img snapshot2.img
>
>Note that you should not write to snapshot1.img anymore.  However, you
>could say:
>
>qemu-img create -f qcow2 -b snapshot1.img snapshot2a.img
>qemu-img create -f qcow2 -b snapshot1.img snapshot2b.img
>
>Don't write to snapshot1.img but you can run VMs using snapshot2a.img
>and snapshot2b.img independently.
>
>> Also, is there a way to generate 100% snapshot of the original volume
>>(an
>> exact replica), so that a 40G original results in a 40G snapshot?
>
>cp original.qcow2 clone.qcow2
>
>Stefan