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

From: Eric Blake
Subject: Re: [Qemu-discuss] [libvirt-users] libvirt live migration, qcow2 image, nbd server
Date: Fri, 13 Feb 2015 13:01:56 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

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).

>>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.

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

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