There's an easy test to check for the difference of redundancy wasted for availability (RAID) and backup: Just delete everything by accident or intention. On a RAID-1 you have two empty disks afterwards so if you did it correctly and do backup it's now time to restore from the backup. If you confused availability with data protection (and did not backup your data) then now your data has gone.
i used freenas before, which i only have to save the configuration file to backup the system. The data are backup via raid1. Sure if i delete my data, i will loose them. But i can live with it.
But on my new system, i don't have enough RAM to use freenas.
Do you have a guide to manuelly backup via rsync every night? i would use 1 disk as primary disk and 1 as backup disk. Every night i want to copy only new files. Is there a plugin for such use case?