RAID would protect only from a HD failure, not from a failure higher up the chain as any corrupted data will get written to *both* drives and you are stuffed.
Since the vast majority of data loss cases are either the user doing something, or a program misbehaving, a backup is far more useful than RAID.
An Adaptec controller should be OK but I have found that the IDE-RAID or SATA-RAID controllers found on a lot of motherboards are lousy. I lost everything a few months ago when one drive in a mirrored pair failed, and now I don't bother with RAID.
The problem is that backing up is very expensive. One needs a tape drive - after all these years there still isn't a better solution for the amount of data one can have an a HD.