[libvirt-users] how "safe" is blockcommit ?

[Lentes, Bernd]

Hi,

currently i'm following https://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit. I 'm playing around with it and it seems to be quite nice.
What i want is a daily consistent backup of my image file of the guest.
I have the idea of the following procedure:

- Shutdown the guest (i can live with a downtime of a few minutes, it will happen in the night).
  And i think it's the only way to have a real clean snapshot
- create a snapshot with snapshot-create-as: snapshot-create-as guest testsn --disk-only
- start the guest again. Changes will now go into the overlay, as e.g. inserts in a database
- rsync the base file to a cifs server. With rsync not the complete, likely big file is transferred but just the delta
- blockcommit the overlay: blockcommit guest /path/to/testsn --active --wait --verbose --pivot
- delete the snapshot: snapshot-delete guest --snapshotname testsn --metadata
- remove the overlay

Is that ok ? How "safe" is blockcommit on a running guest ? It's possible that during the rsync, when the guest is running, some inserts are done in a database.
Is it safe to copy the new sectors (i assume that's what blockcommit does) under a running database ?
Or is it only safe doing blockcommit on a stopped guest ?

Thanks for any answer.

Bernd

P.S. Is the same procedure possible when the guest disk(s) reside directly in a plain logical volume, without a file system in-between ?



-- 

Bernd Lentes 
Systemadministration 
Institut für Entwicklungsgenetik 
Gebäude 35.34 - Raum 208 
HelmholtzZentrum münchen 
[ mailto:bernd.lentes at helmholtz-muenchen.de | bernd.lentes at helmholtz-muenchen.de ] 
phone: +49 89 3187 1241 
fax: +49 89 3187 2294 
[ http://www.helmholtz-muenchen.de/idg | 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: MinDir'in Baerbel Brumme-Bothe
Geschaeftsfuehrer: Prof. Dr. med. Dr. h.c. Matthias H. Tschoep, Heinrich Bassler, Dr. rer. nat. Alfons Enhsen
Registergericht: Amtsgericht Muenchen HRB 6466
USt-IdNr: DE 129521671