NAS-to-NAS backup

I have used an RN102 and an RN202 to back up a legacy NAS.  I was backing up a pro-6, but the same methods do work with v1 and v2 NAS.

I use the built in backup jobs on the destination NAS (though running them on the source NAS will also work).  I use rsync, since that is the most efficent way to make robust incremental backups.  Often you get better results using IP addresses (and not the remote hostname).

I always use one backup job for each share.  Personally I don't use the "home" folders, though you can back them up to the OS 6 system if you like.  

FWIW, the RN102 and the RN212 are faster than your aging duos.  Plus SMB1 is being deprecated by Microsoft, and that's the only SMB version that the duos support.  Personally I'd make the OS 6 units your primary NAS, and use the two duos as the backup.  You can then disable SMB altogether on the duos (just using rsync).  That can give you a bit more protection from ransomware.