"borg compact --dry-run --verbose" could show the estimated freed space

[adrian-amaglio]

I’d like to measure compaction freed space before actually removing segments to detect massive data loss or gain (due to backup suppression or cryptolocker attack).
In my case, this information could trigger an alert and ask for manual confirmation of data deletion.

Currently, this command outputs nothing borg compact --dry-run --verbose <repo>.
It is on purpose if I understand #8300 correctly.

Is it technically possible and would it be useful to have a dry compact that actually estimate freed space?

To allow fast dry scripts as the one mentioned in #8300 it could be another command, doing some work but not actually deleting data.

Thanks for your borgbackup work <3

[ThomasWaldmann]

I don't think one should put effort into that part of the code right now, it may change significantly from borg1 to borg2.

Also, to make sure your backups are ok, maybe rather focus on whether what you have (== the not deleted backups) is as expected (== contains the data it shall contain).

Compaction is only a cleanup step, it physically removes data that is not used anymore (usually because the archive referencing the data already was deleted).