The benefit of using something fancier than rsync is that you get a point-in-time recovery capability.
For example, if you switch the enclosures weekly, rsync gives you two recovery options: restore to yesterday’s state (from the enclosure not in the safe) and restore to a state from 2-7 days ago (from the one in the safe, depending on when it went into the safe).
Daily incremental backups with a fancy tool like dar let you restore to any previous state. Instead of two options, you have hundreds of options, one for each day. This is useful when you mess up something in the archive (eg: accidentally delete or overwrite it) and don’t notice right away: It appeared, was ok for awhile, then it was bad/gone and that bad/gone state was backed up. It’s nice to be able to jump back in time to the brief it-was-ok state & pluck the content back out.
If you have other protections against accidental overwrite (like you only back up git repos that already capture the full history, and you git fsck
them regularly) — then the fancier tools don’t provide much benefit.
I just assumed that you’d want this capability because many folks do and it’s fairly easy to get with modern tools, but if rsync is working for you, no need to change.
There are so many ways do handle backups, so many tools, etc. You’ll find something that works for you.
In the spirit of sharing a neat tool that works well for me, addressing many of the concerns you raised, in case it might work for you too: Maybe check out git annex. Especially if you already know git, and maybe even if you don’t yet.
I have one huge git repository that in spirit holds all my stuff. All my storage devices have a check-out of this git repo. So all my storage devices know about all my files, but only contain some of them (files not present show up as dangling symlinks). git annex tracks which drives have which data and enforces policies like “all data must live on at least two drives” and “this more-important data must live on at least three drives” by refusing to delete copies unless it can verify that enough other copies exist elsewhere.
git annex fsck
on a drive will verify that