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

[Eric Blake]

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).

> 
>>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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