Hello Stefan,
But how can I explain that both backups are identical in size and content as
soon as I export them as .zip or .tar?
At most, it happens that the backups differ in one or two lines in a log file,
but are otherwise completely identical.
Nevertheless, BackupPC v4 displays something completely different in the
overview.
I can just suppose that is is related to the following:
(https://backuppc.sourceforge.net/BackupPC-4.0.0.html):
[...]
This is the first release of 4.0, which is a significant rewrite of
BackupPC. This section provides a short overview of the changes and
features in 4.0.
Here's a short summary of what has changed in V4:
No use of hardlinks (except temporarily to do atomic renames).
Reference counting is handled at the application level in a batch manner.
Backups are stored as "reverse deltas" - the most recent backup is
always filled and older backups are reconstituted by merging all the
deltas starting with the nearest future filled backup and working
backwards.
This is the opposite of V3 where incrementals are stored as "forward
deltas" to a prior backup (typically the last full backup or prior
lower-level incremental backup, or the last full in the case of rsync).
[...]
I think you cannot properly compare v3 with v4 other then starting from a
system that was never backed up before.
.zip and .tar do not know anything about the history of the files they
deal with, or about previous backups.
In contrast, BackupPC focuses and puts a lot of effort on keeping track of
what was previously seen already, to avoid duplication.
Good luck,
Iosif Fettich
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