On Wednesday 03 September 2008 14:17:56 James Cort wrote:
> Kern Sibbald wrote:
> > I am not 100% sure what to do to resolve this issue.  I suppose one could
> > run a Migration job to "move" the Virtual Backup back to the Pool from
> > which it originally came, then the next Virtual Backup would work fine
> > (the same as the first one), but that sounds a bit kludgie.
>
> I'm speaking in theory here because I'm not familiar with the code; I'm
> just a satisfied user of bacula for a couple of years now.
>
> I'm thinking if immediately you start a virtual backup, you set up a
> temporary virtual pool to which you migrate any media in the pool used
> for storing virtual backups and migrate them back again when the job
> completes.
>
> But then you have to deal with what happens if the director dies or is
> killed part-way through a virtual job.
>

Well, if you mean changing the pool in which the Media reside rather than a 
Migration job, what you describe would not be hard to do.  The problem is 
that regardless of what pool the Volumes are in, if the Volume name remains 
the same, the potential deadlock will remain because the deadlock occurs at 
the Volume level.  For example, assume you first write your data to a disk 
file, then you run a Virtual Backup and put that backup on a single drive 
tape.  You can then move that tape back to the original pool, then you run a 
Virtual backup.  At that point, Bacula will want to read from one pool and 
write to another pool so it will be a question of different volumes, but if 
the original Virtual backup was made to a single drive tape, you will be in a 
deadlock anyway because you cannot read tape 1 and write tape 2 on the same 
drive at the same time :-(

The problem if deadlocks and ensuring that Bacula does not get into them is 
relatively simple as long as you work with two different pools that use 
volumes on different drives.  Once you start moving volumes from one pool to 
another, you expose yourself to potential deadlocks ...


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