From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kevin Wolf <kwolf@redhat.com>
Subject: Re: Swap virtio images
Date: Wed, 06 Jun 2012 16:27:27 +0200
Message-ID: <4FCF68CF.3060008@redhat.com>
References: <CAA-N7kyFr5S_8dQieWVRS7L6noTRtE+NHmRv8zpevvL35d+6=w@mail.gmail.com>
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Cc: kvm@vger.kernel.org
To: "Iain J. Watson" <lists@ij-watson.co.uk>
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Am 06.06.2012 15:35, schrieb Iain J. Watson:
> Hello,
> 
> I am trying to find a way to use backing files to make snapshots of
> running VMs. The idea is I pause the VM, use qemu-img to create a new
> disk file with the currently used file as a backing file, swap the
> images then unpause the VM.
> 
> Commands would be something like:
> 
> ----------
>   (qemu) stop
>   (qemu) drive_del virtio0
> 
>   $ qemu-img create -f qcow2 -b os-disk-0.qcow2 os-disk-1.qcow2
> 
>   (qemu) drive_add 0 file=os-disk-1.qcow2   # I'm not 100% sure on the
> drive_add syntax
>   (qemu) c
> ----------
> 
> If I try and do this just now I get the error "Can't hot-add drive to
> type 7" when running the drive_add command.
> 
> Is there another way to achieve this? Is this something that could
> potentially be added or would architecture not support what I'm trying
> to do?

You're looking for the 'snapshot_blkdev' monitor command:

(qemu) snapshot_blkdev virtio0 os-disk1.qcow2 qcow2

Kevin