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Re: [Bacula-devel] [Bacula-users] Vbackup feature

Kern Sibbald wrote:
> Hello,
> I'm a bit burned out from intensive bug fixing over the last couple of months, 
> so decided to do something totally new yesterday.  I started implementing 
> what I call Virtual Backup or Vbackup, which is essentially project #3 "Merge 
> multiple backups (Synthetic Backup or Consolidation)".
> In attempting to implement it, I've realized a few things: 
> 1. It is probably better to implement it as a new "level" under the normal 
> Backup code, for example "level=vbackup".  The resulting output will be  
> recorded in the catalog as a "Full".
> 2. In most all respects it must behave much like a Migration job in that it 
> does not use a FD, it reads an existing set of backups, and writes them to a 
> new Volume.
> 3. One difference from a Migration job is that all the old jobs remain 
> unchanged (i.e. like a Copy).  
> 4. Another difference is that it has many fewer features in that it simply 
> finds all the current backup records and copies them.  There are no 
> complicated selection criteria.
> 5. Like the Migration and Copy jobs, the input Pool (from where it reads the 
> currently backed up data) and the output Pool (where it writes the merged 
> data) must be different.  This ensures that the job does not attempt to read 
> and write to the same device, which just will not work.
> Well the problem with the above -- principally item #5 is consider the 
> following:
> You have a job J1, which does a Full, one or more Diff backups, then any 
> number of Inc backups all going to Pool P1.  At some point in time (possibly 
> via the Schedule), you run a vbackup level, so it finds all the current 
> backup files (Full, last Diff, and all later Inc) and copies the data from 
> the input Pool (P1) to the output Pool (P2).
> Now, if you then redo a normal Full backup and restart with Diff and Inc jobs 
> again, all will work. 
> However, it is much more likely that you will then continue doing incremental 
> backups (no more Full or Diffs).  At some point later, you want to do another 
> vbackup to "consolidate" all the Inc backups, and now the process fails, 
> because you are going to need to read from Pools P2 (Full produced by the 
> vbackup) and P1 (new Incs), and you will attempt to write to P2, which will 
> not work.
> Thus without some other mechanism to move Volumes from Pool to Pool, a setup 
> like described above won't work, and I suspect this is what will be done the 
> most frequently (i.e. do only one Full and there after vbackups when there 
> are enough Incs to warrant a consolidation).
> Any comments?

Why not always write vbackup jobs to a volume in a "special" pool first? 
When writing to the volume(s) in the special pool is completed, either 
the volume(s) could be moved from the special pool to the destination 
pool specified by the job, or the entire vbackup job could be migrated 
to the destination pool. The former would be faster, but would likely 
waste space due to fragmentation if the destination pool was only used 
for vbackup jobs. However, the destination pool could be the same pool 
used for normal backups, and remaining volume space would be usable by 
normal jobs. In either case, all normal pools (except the special pool 
and the Scratch pool) could then be used for input, including the 
destination pools of previous vbackup jobs. I would envision putting 
vbackup jobs into the same pool I put normal full backup jobs.

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