Automatic backup and an easily documented restore process are not two things that go together for linux noobs.
Amen...
How can I automatically backup my USB-Drive or SSD with the OMV-system to another NAS and how exactly is the restore process? All this for someone with 5 thumbs in every hand regarding LINUX.
The automatic backup part of this is relatively easy. The restoration process is another matter altogether. There are a lot of variables induced by the way it's set up by a user, hardware considerations, the type of restore, etc.
If you're wobbling with Linux, your best bet is to go with thumbdrives and off-line cloning. A walk through of cloning and the restoration process can be found -> here.
When looking at this topic and trying to come up with a backup / restore process (and a written procedure) that all could easily accomplish, cloning thumbdrives was the best thing I could come up with.