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?
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