Hi,

Matthias Meyer wrote on 2009-07-05 21:14:57 +0200 [Re: [BackupPC-users] How to 
reuse already saved data until an interrupted incr backup]:
> > I use BackupPC 3.1 and rsyncd.
> > If an incr Backup aborts, e.g. because of lost network connections, all of
> > the data, which was copied into the /new directory, will be deleted.
> > The next time an incr backup runs, all the work (compare and transfer)
> > must be done again.
> > 
> > What is the reason for this behavior?

that is a good question, but it is difficult to answer without a close look at
the code. Without looking at the code, I'd *guess* it might be the same reason
as for not using the previous backup as reference for any backup. Strictly,
completing a partial level N backup would give you a level N+1 backup, because
the reference is (partly) a (partial) level N backup. Yes, I know, nobody
except me takes that seriously.

> > Is there a posibility to save the already saved data and reuse it for the
> > next backup in a similiar way as in interupted full backups?

No.

> [...]
> In the next step I will try to move the /new directory to a /<number>
> directory, update the /backups file and run BackupPC_link during the
> DumpPostUserCmd.
> 
> Is there any reason to not do that?

This is not a good question. The answer is, obviously, "yes" - otherwise
BackupPC would already be doing that by default (it's not as though that would
be difficult for BackupPC - it would just require *not* handling the error).
The question "why shouldn't I do that" is not much better. Isn't the fact that
you shouldn't good enough? But if you insist on an answer ...

1. You will have something that looks like a successful backup but isn't. You
   just might be able to remember that now, but what happens in two weeks
   time, when you need to restore files?
   I don't exactly know what such a backup would look like, but there are
   basically two possibilities:
   a) The backup view contains all files processed (i.e. found to be "same" or
      transferred). All files beyond the point where it failed are missing.
   b) All files beyond the point where it failed are identical to their state
      in the reference backup.
   I presume it's case a, but if it's case b, things get even more awkward.
   You see what seems to be a complete backup, but some files are current and
   some might be older versions than in preceeding incrementals. Case a would
   at least show you an incomplete backup when you are browsing it (presuming
   enough is missing for you to notice).

2. What is run next? That depends on your setup. If it's an incremental of the
   same (or lower) level, all changes are re-transferred, so you gain nothing.
   You simply end up with a bogus backup in your history.
   On the other hand, if it's a full or an incremental of *higher* level (you
   have a level N backup in your 'backups' file, so BackupPC would do a level
   N+1 if that is what you configured), the backup will need to re-transfer
   *all files you missed on the partial* (at least in case a above), meaning
   you probably lose (much) more than you gain, aside from also having a bogus
   backup in your history.


Beside that, as Les said, it's either infrequent enough not to be important,
or you should be fixing something rather than kludging around a real problem.

Regards,
Holger

P.S.: Doing something because you don't understand why not to suggests you
      have more relevant questions to ask than this one. Then again, maybe
      you *are* asking part of that question. Maybe your current problem is
      one aspect of an answer you understand? More clearly: maybe you should
      not be using incremental levels because you'll end up with failing
      incremental backups which will not be completed. But that's just a guess
      from the parts of the puzzle you decided to give us. It's certainly
      *not* a general recommendation against incremental levels. There are
      simply cases where you should be doing frequent full backups.

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