Because Duplicati is basically an “incremental forever” type of backup solution, it won’t want you to rotate the backup destination drive. It’s just not built for that type of usage.
If you really want to take a physical copy off site, what you might consider is something like this:
- Leave your main backup drive in place at all times so as not to confuse Duplicati
- Every so often plug in your second backup drive and synchronize the data from the main backup drive
- You’ll want to sync everything exactly - including any file deletions that have happened on the main backup drive (
robocopy /miris your friend)
One caveat is that the local database will get out of sync with this secondary backup pretty quickly. Not a showstopper but it may make restores more complicated (you may need to rebuild the database from the secondary backup copy).