libvirt users - Apr 2019 - Re: is it possible to create a snapshot from a guest residing in a plain partition ?

Hi,

i can store the disk of a guest in a plain partition which isn't formatted.
That's no problem, i did it already several times, although the promised
speed increase didn't appear.

But is it possible to create from such a guest a snapshot in a .sn file using
virsh ?

Regards,


Bernd

-- 

Bernd Lentes 
Systemadministration 
Institut für Entwicklungsgenetik 
Gebäude 35.34 - Raum 208 
HelmholtzZentrum münchen 
bernd.lentes@helmholtz-muenchen.de 
phone: +49 89 3187 1241 
phone: +49 89 3187 3827 
fax: +49 89 3187 2294 
http://www.helmholtz-muenchen.de/idg 

wer Fehler macht kann etwas lernen 
wer nichts macht kann auch nichts lernen
 

Helmholtz Zentrum Muenchen
Deutsches Forschungszentrum fuer Gesundheit und Umwelt (GmbH)
Ingolstaedter Landstr. 1
85764 Neuherberg
www.helmholtz-muenchen.de
Aufsichtsratsvorsitzende: MinDirig'in Petra Steiner-Hoffmann
Stellv.Aufsichtsratsvorsitzender: MinDirig. Dr. Manfred Wolter
Geschaeftsfuehrung: Prof. Dr. med. Dr. h.c. Matthias Tschoep, Heinrich Bassler,
Kerstin Guenther
Registergericht: Amtsgericht Muenchen HRB 6466
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On 4/3/19 9:44 AM, Lentes, Bernd wrote:
> Hi,
> 
> i can store the disk of a guest in a plain partition which isn't
formatted.
> That's no problem, i did it already several times, although the
promised speed increase didn't appear.
> 
> But is it possible to create from such a guest a snapshot in a .sn file
using virsh ?
It is possible to create an external snapshot (an internal one is not
possible, unless you stored the guest disk as qcow2 format embedded
inside the partition rather than directly as raw format).  Note that
when you create an external snapshot, the partition becomes a read-only
point in time (no further updates to that partition), and your new
file.sn qcow2 wrapper file created by the snapshot operation stores all
subsequent guest writes. (Well, unless you decide to do a commit
operation to push the changes from the overlay back into the base file
and get rid of the overlay)


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

----- On Apr 3, 2019, at 5:27 PM, Eric Blake eblake@redhat.com wrote:


> It is possible to create an external snapshot (an internal one is not
> possible, unless you stored the guest disk as qcow2 format embedded
> inside the partition rather than directly as raw format).  Note that
> when you create an external snapshot, the partition becomes a read-only
> point in time (no further updates to that partition), and your new
> file.sn qcow2 wrapper file created by the snapshot operation stores all
> subsequent guest writes. (Well, unless you decide to do a commit
> operation to push the changes from the overlay back into the base file
> and get rid of the overlay)
Hi Eric,

thanks for your answer.
i tried it:

virsh # snapshot-create-as --disk-only --name sn --domain sim
error: unsupported configuration: source for disk 'vdb' is not a regular
file; refusing to generate external snapshot name

This is the snippet from the conf for the guest:

<disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none'
io='native'/>
      <source dev='/dev/vg_san/lv_sim'/>
      <backingStore/>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x00'
slot='0x06' function='0x0'/>
    </disk>

I'm running SLES 12 SP4 with libvirt 4.0.0-6.13.x86_64.

Any ideas ?


Bernd
 

Helmholtz Zentrum Muenchen
Deutsches Forschungszentrum fuer Gesundheit und Umwelt (GmbH)
Ingolstaedter Landstr. 1
85764 Neuherberg
www.helmholtz-muenchen.de
Aufsichtsratsvorsitzende: MinDirig'in Petra Steiner-Hoffmann
Stellv.Aufsichtsratsvorsitzender: MinDirig. Dr. Manfred Wolter
Geschaeftsfuehrung: Prof. Dr. med. Dr. h.c. Matthias Tschoep, Heinrich Bassler,
Kerstin Guenther
Registergericht: Amtsgericht Muenchen HRB 6466
USt-IdNr: DE 129521671