Thomas Birnthaler wrote at about 00:41:26 +0100 on Friday, January 9, 2009:
 > Wow Tino,
 > 
 > your faster anwering than I'm able to question ;-)
 > 
 > > Your web view would become inconsistent (e.g. deleted files becoming
 > > visible again).
 > Ok, this seems to be a case we forgot ;-(
 > But if this doesn't matter to us, is it then okay to delete any backup?
You also have the problem that you are missing new changes so that you
will have an inconsistent system state.
 > Do the GUI and the creation of new backups work and don't throw errors?
 > 
 > By the way: How are deleted files represented?
They are given a type=10 deleted attribute in the corresponding
directory attrib file.
 > I argue they are just missing in the respective backup hardlink
 tree.
That would be wrong -- you need to explicitly notate that files are
deleted because otherwise the absence of a file is interpreted to mean
that you inherit the file from earlier versions.
 > So if you delete the backup hardlink tree, the "holes" disappear?
Nope -- see above.
 > 
 > > > In both cases only changed/new files use disk space according to the
 > > > hardlink concept of BackupPC.
 > >
 > > Yes. Fulls need some more space because they are completely filled, that
 > > is, all directories contain hardlinks to all the files, whereas
 > > incrementals only contain hardlinks to new and changed files -
 > > filesystem-wise they've got holes which are filled by the CGI.
 > But this is just management space (directories and their dentries) --- which 
 > uses of course some inode and data space. No additional data space and inode 
 > space is needed for the real files in full backups compared to a incremental 
 > backup. Is that correct?
Nope. Zero length files are given their own inodes. Also symbolic links are
represented as files (which are non-zero length). Now this might not
make a measurable difference but it is important to understand
what BackupPC is doing before you generalize or make assumptions.

 > 
 > If this is the case we think about doing full backups all the time.
 > So deletion of backups is ok then too.
 > 
 > > > We have also detected, that in some cases incremental backups need much
 > > > more time than full backups (factor 3-5) This sounds odd to us.
 > >
 > > What transfer method are you using?
 > rsync over GBit networks between Linux machines and also between MacOS 
 > machines. In both cases that effect happens.
 > 
 > Thomas Birnthaler
 > -- 
 > OSTC Open Source Training and Consulting GmbH / HRB Nuernberg 20032
 > tel +49 911-3474544 / fax +49 911-1806277 / http://www.ostc.de
 > Delsenbachweg 32 / D-90425 Nuernberg / Geschaeftsfuehrung:
 > Thomas Birnthaler / +49 171-3047465 / tb AT ostc DOT de / pgp 0xFEE7EB4C
 > Hermann Gottschalk / +49 173-3600680 / hg AT ostc DOT de / pgp 0x0B2D8EEA
 > 
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