Hi,

Michael Stucki wrote on 2008-07-23 14:27:17 +0200 [[BackupPC-users] Change 
RsyncShareName - will BackupPC reuse existing backup data?]:
> I'm backing up a rather huge system which I had synced with rsync before.
> 
> [...] I had to change XferMethod and RsyncShareName. [...]
> 
> The backup seems to work will, as the data gets copied. However, since it
> takes extremely long, I have the impression that the old backups are not
> found anymore, and the full data is transferred again.
> 
> I have no proof if the old data is really ignored, just think that it takes
> way too long. Can anyone confirm this?

yes, that is correct. The pooled data is re-used, i.e. no extra space is taken
up on the BackupPC server, and even re-compression of the data is unnecessary
(the pooled copy is found and decompressed - provided you are using
compression, that is). But it needs to be re-transferred first. There is no
way for BackupPC to know that the 'share' "foo" used to be named "bar", even
if it's obvious to you, so the old contents cannot be used as a reference to
speed up the transfer. And no, it is not possible to use the pool file as
reference, because you need part of the file contents and the file length to
determine the possible pool files, and by the time the BackupPC server has
that data, it's too late to select a reference file, because the transfer of
the file is already in progress.

> Is it a bug?

No.

> It would have been very easy if rsyncd allows module names to be named
> like paths, e.g. "/". However, as this doesn't work I was forced to change
> the RsyncShareName...

I'm no rsyncd expert, but I believe I've read of people using rsyncd modules
named like paths. Aside from that, why didn't you use rsync over ssh or sudo
instead of rsyncd for the initial local backup (of course the paths would still
have to match, but maybe chroot can help there)? That seems even more
straightforward than naming the rsyncd module according to what the real path
is.

Regards,
Holger

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