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Re: [Qemu-discuss] [libvirt-users] libvirt live migration, qcow2 image,

From: Edward Young
Subject: Re: [Qemu-discuss] [libvirt-users] libvirt live migration, qcow2 image, nbd server
Date: Fri, 13 Feb 2015 15:24:56 -0600

On Fri, Feb 13, 2015 at 2:01 PM, Eric Blake <address@hidden> 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://
> tcp://"
> 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.


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

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