The thing to keep in mind here is that RAID is not a replacement for a good (and tested) backup. RAID is intended for those applications where up time is paramount, it allows for the failure of one (or more depending on the level) drive, and the hot replacement of same, without taking the storage volume off line. Do not use RAID0 (which is not really RAID as there is no redundancy) to store anything you are not willing to lose should a drive fail.
But say I have like 9 drives. Am I better served by putting 6 of them in a RAID1 and having 3 as a backup, having 3-5 in JBOD and 4-6 as backup, or having 6 in RAID5/6 and 3 backup?