[Borgbackup] purge not deleting data?

[Thomas Waldmann]

Hi,

> every few days, i see that borg prune does not appear to purge data from the repos,
> and for my curiosity it happens for all repos at the same day/backup-run

Well, guess you do not create a borg archive every day?

E.g. because your cronjob does not run sundays or so?

Or, due to other circumstances (e.g. machine powered off) it did not
happen to make a backup every day?

It could also be just a not-so-obvious effect of implementing your prune
policy, like the different parts (daily, weekly, monthly, ...) interfering.

> - though rsync tells it did delete files from the rsync copy.

That is completely unrelated, it just reduces total size and count of
files in your backup data source.

> so i wonder under which circumstances borg prune skips deleting files !?

borg prune deletes ("thins out") backup archives following the policy
you give to it. It just decides which backup archives to keep / not to
keep, so the policy you gave is implemented. If you give -v --list, it
will spill out the result of that decision.

As a consequence of archives getting deleted (if your repo is not
append-only) it will also usually reduce your overall repo size IF it
decided to delete at least 1 old archive.

> as the repos were created at different points in time i cannot explain this to me, maybe someone has a clue how this can be explained or analyzed?

The effects of non-trivial purge policies (maybe combined with not
making a backup every day) are often a bit hard to explain.

A while ago I tried to explain prune policies better and made a
graphical example, see there:

https://github.com/borgbackup/borg/blob/1.0-maint/docs/misc/prune-example.txt

BTW, I've seen you use d-m-y for dates, that is not the best way to do
it as it does not sort correctly. Maybe rather use y-m-d, if possible.

Cheers, Thomas