On Wed, Jan 12, 2011 at 11:41, Graham Keeling <[email protected]> wrote:
> On Wed, Jan 12, 2011 at 10:54:13AM -0600, Mark wrote:
> > On Wed, Jan 12, 2011 at 9:35 AM, Valerio Pachera <[email protected]>
> wrote:
> >
> > >
> > > SCOPE: We want the possibility of restore any file till 2 weeks ago.
> > >
> >
> > ...
> >
> >
> > > at sunday of the third week, the first full backup get overwritten.
> > >
> > > _ _ _ _ _ _ | _ _ _ _ _ _ |
> > >
> > > This means that, of the first week, I can only restore file present in
> > > the incremental backup.
> > > In other words I do not have a cicle of 2 weeks but 1.
> > >
> > >
> > When your first week's full backup gets overwritten, what are those
> > incremental backups "incremental to"? What's you're describing sounds
> like
> > what I expect fulls and incrementals to be. When you overwrite the full,
> > you've essentially orphaned the incrementals that were created based on
> that
> > full backup.
>
> Bacula doesn't prevent backups that other backups depend on from being
> purged.
>
> If there is no previous Full before the Incrementals, you cannot easily
> restore
> the files in the Incrementals. You have to extract the files from the
> individual volumes with the 'bextract' command.
>
> It also doesn't have anything that indicates that a particular backup was
> based on another particular backup. It calculates everything based on
> dates.
>
> So, if an Incremental from the middle of a sequence got purged (somehow),
> bacula won't notice and will happily restore from the latest Incremental.
> It is good that you can restore something, but bad because the files you
> get
> back may well not be the same as the ones that were on your client machine
> on
> the day that the Incremental was made.
>
>
> Anyway, this all means that you need to set your retention times very
> carefully.
>
> If you set them so that they cover the periods that you're worried
> about - like Valerio's example of wanting to restore from two weeks back...
> F I I I I I I F I I I I I I I F
> ...you might decide to set the retention of Fulls to 3 weeks.
> But be careful! If, for some reason, a Full backup fails, time will march
> on
> and you will end up having a Full that other backups depend on getting
> purged
> (imagine the 2nd 'F' in the sequence above being missed out).
>
>
> I actually wrote a patch that enforces that bacula only purges backups
> that other backups don't depend on. But it makes some assumptions about
> your
> setup. It assumes that you are using one job per volume and it assumes that
> you are not using Job / File retentions (ie, you have set them very high)
> and
> instead rely purely on Volume retentions.
>
> So, if your retention is set to one week, the purge sequence will be like
> this
> (with new backups being made on the right).
>
> F I I I I I I F I I I I I I F
> F I I I I I F I I I I I I F I
> F I I I I F I I I I I I F I I
> F I I I F I I I I I I F I I I
> F I I F I I I I I I F I I I I
> F I F I I I I I I F I I I I I
> F F I I I I I I F I I I I I I
> F I I I I I I F I I I I I I F
> F I I I I I F I I I I I I F I
>
> This also suffers if a Full backup is missed, because you end up having to
> keep more old backups.
>
> I can upload this patch if it is interesting to people.
>
>
>
> P.S. One last thing - try not to worry about what bacula does if your clock
> somehow goes wrong and decides that it is 2037. Or 1970. Or last week. :)
>
>
This is supposedly better in the upcoming version at least in regards to
pruning. If they have gotten the pruning to work properly on pools as well,
it could potentially make a lot of lives easier. I personally never
understood the logic behind the implicit assumptions that the restore and
backup algorithms make in regards to job tree structure, but at least things
are progressing. I'm just still hoping that they will some day include a
more realistic concept for management of locations of data and the
implications related to backups / restores.
-Blake
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