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

[Edward Young]

On Fri, Feb 13, 2015 at 2:01 PM, Eric Blake <eblake at redhat.com> wrote:

> On 02/12/2015 07:41 PM, 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.
> >
>
> Was that error printed by the source or the destination qemu? It may be
> a bug in libvirt for not explicitly requesting raw (we DO want the NBD
> server to be raw, but need to be explicit so as to avoid unsafe probing).
>

 This error was printed from the source in deed.


>
> >
> >>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.
>
> Just because the underlying file on the disk is qcow2 does not impact
> what the NBD is serving - the NBD connection MUST be raw, unless you
> have a funky situation with a qcow2 file whose contents are also a
> nested qcow2 encoding of data.
>
OK, I got it.

Thanks!
Ed


>
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
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