A RAID is supposed to be a fault tolerant "live" working repository for your files, not a backup. A backup, regardless of medium (even if it's to a RAID volume) should never be used "live" - only a backup (or restore) operation should touch those volumes. When not performing a backup or restore, the medium should preferably be moved off site. At least put somewhere safe, away from your live volumes.

If I move to something like the ReadyNAS Pro, I'm not likely to have enough external volumes for a 1:1 backup, but all my critical assets will be covered, including music. Things like TV recordings I'll have to leave to chance.