[libvirt-users] libvirt live migration, qcow2 image, nbd server

[Kashyap Chamarthy]

On Fri, Feb 13, 2015 at 01:03:49PM -0700, Eric Blake wrote:
> On 02/13/2015 03:15 AM, Kashyap Chamarthy wrote:
> > On Thu, Feb 12, 2015 at 08:41:31PM -0600, Edward Young wrote:
> >> Hi all,
> >>
> >>
> >> When I live migrate a vm using
> >>
> >> "migrate --live --copy-storage-all mig-vm qemu+ssh://192.168.1.3/system
> >> tcp://192.168.1.3"
> >>
> >>
> >> I got the following error
> >>
> >>
> >>              WARNING: Image format was not specified for
> >> 'nbd://node2:49155/drive-virtio-disk0' and probing guessed raw.
> >>
> >> 258          Automatically detecting the format is dangerous for raw
> >> images, write operations on block 0 will be restricted.
> >>
> >> 259          Specify the 'raw' format explicitly to remove the restrictions.
> >>
> >>
> >> >From the error itself, I can tell that nbd server treat this image as raw,
> >> rather than qcow2. My platform is libvirt+qemu. the image type of this vm
> >> is indeed qcow2. I do not know how to let nbd know this image format.
> > 
> > Hmm, I wonder if `virsh --migrate` should have a --format (or -F) option
> > that one can specify the format. Let's see what Eric Blake and others say.
> 
> No. The format used by the NBD connection under the hood is not
> user-visible (for that matter, there may be more than one disk being
> migrated, and a single 'migrate --format' would NOT be sufficient to
> cover the case where multiple disks for the guest have different formats
> on the host).  I think that it is merely a case where libvirt itself
> needs to explicitly tell qemu that the NBD server it is setting up under
> the hood will serve raw data, as there is no mention of the NBD server
> on the command line.

Thanks for the explanation, it's at-least very clear why the "--format"
in this case is not sufficient at all.


-- 
/kashyap