[Borgbackup] When is the cache rebuilt?

[Thomas Waldmann]

> I don't use different users, and my script sets BORG_CACHE_DIR so the
> cache location wouldn't depend on that (I think).
> 
> It occurs to me that maybe I have misidentified what's going on as a
> cache rebuild. What I see is, I'm backing up when very little has
> changed, but borg is spending a lot of time on files that haven't
> changed.

Use -v --list to clearly see what they are classified as (see docs what
the letters mean).

> So I'm guessing that it's checksumming all the files, which it doesn't
> usually do.

When you did an upgrade from 1.0 to 1.1, that will happen once for all
files due to the changed files cache content (1.0: mtime,inode,size
1.1:ctime,inode,size).

> So maybe the cache is fine, but something else is making
> borg think it needs to checksum files that haven't changed?

If it is happening withing 1.1 backups (not directly after switching
from 1.0), it could be that you did e.g. some chown -R and that changed
the ctime.

Or you have a filesystem that has no stable inode numbers, like some
network filesystems.

Change detection is based on the 3 values I mentioned above. If they did
not change, borg won't chunk. If at least one of them changed, it will
assume that the file might have changed contents.


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