libvirt users - Feb 2015 - Re: libvirt live migration, qcow2 image, nbd server

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.


Thanks!

Ed

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.


-- 
/kashyap

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

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.

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

On Fri, Feb 13, 2015 at 2:01 PM, Eric Blake <eblake@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
>
>