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

From: Jes Sorensen
Subject: Re: [Qemu-devel] Issue with snapshot outside qcow2 disk - qemu 0.14.0
Date: Thu, 10 Mar 2011 10:32:36 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc14 Thunderbird/3.1.7

On 03/10/11 10:27, Stefan Hajnoczi wrote:
>> Is Scenario 2 safe where in the copying the snapshot outside the original 
>> qcow2 is being executed with the VM running. This is because if this is safe 
>> then this could be an approach as it would not require a long downtime for 
>> the VM.
> There is no guarantee that qemu-img will work on an image file that is
> open by a running VM.

I think the guarantee here is that you're guaranteed it will go horribly
wrong if you try to do so.....

> I have CCed Jes who has been working on a live snapshot mechanism.  He
> recently added the snapshot_blkdev monitor command that takes a
> snapshot of a block device while the VM is running.  A new image file
> is created based off the original image file (which will no longer be
> modified), all new disk writes go to the new image file.  It is safe
> to perform read-only access to the original image file.  There
> currently is no support to merge the snapshot changes back into the
> original image while the VM is running, but I think that is the next
> planned step.

Yes, keep in mind that the live snapshot is only for external snapshot
files, it doesn't deal with internal snapshots.


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