there are 3 types of situation people often use/confuse for backups:
RAID mirroring (or some other sort of real-time redundancy) – This is not backup! This is fault tolerance. It will not protect you against corruptness or deletions.
Periodic syncing (like the weekly rsync @RBM is doing) – This is backup, but you must catch the need to restore within the period of the sync.
Incremental backup – This is the best, as you get all the benefits of periodic syncing, with multiple cloned copies, and due to deduplication, you can save quite a bit of history going back in time, extending the period in which you need to notice the need to restore.
My suggested NAS setup gets you the first 2, but you have to use a real backup solution for the last. I personally use Crashplan for that. Our longer term plan is to provide this last case built into Roon with bring-your-own-cloud-storage-provider.