Holger writes:
> hmm, that seems to mean that rsync full backups are done relative to the
> previous backup (be that full or incremental). Actually, that is quite
> brilliant. File contents are checked anyway, so why not start with the last
> state, even if that is not fully trusted? It's even known to be more accurate
> than the last full, because the only things that might have been missed are
> changes since the last full ...
>
> This would mean that alternating rsync fulls and incrementals would not
> duplicate any transfers. Nice.
Right on all counts.
This is a new feature in 3.0.0: the reference backup for an
rsync full is the latest backup (of any kind). In 2.x only
the last full was used as the reference for any rsync backups
(whether incremental or full). The only penalty in doing this
is that it takes more server disk accesses to create the "merged"
last backup (ie: the full plus potentially one even several
incrementals if $Conf{IncrLevels} is used).
Actually, in looking at the code I realize that in 3.0.0 the
reference backup for an rsync incremental is the last backup
of the next lower level (this is the same definition used for
tar and smb backups). With the default $Conf{IncrLevels} of 1,
that means each incremental always uses the last full as the
reference.
So these posted results make sense:
> >> For instance, as a test...
> >>
> >> 0 full 10min
> >> Add a bunch of files.
> >> 1 incr 6min
> >> 2 incr 6min
> >> 3 incr 6min
> >> 4 full 0.1min
Each incremental uses the #0 full as a reference, so they each
transfer the same amount of data and take the same time. The
full in 3.0.0 uses #3 (ie: #3 merged with #0) as the reference,
and it doesn't need to transfer nearly as much data. In 2.x
I would expect the #4 full to also take 6 min.
Unless I'm forgetting a good reason why I did it that way, for
rsync I should make the reference backup the most recent backup
in all cases - both full and incremental. It's a pretty simple
change - I'll add it to the todo list for 3.1.0. The logic is
correct as is for smb and tar: the reference backup for an
incremental always is the backup of the next lower level.
Craig
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