I am using HARDWARE RAID with SCHEDULED backups on my home system. The regular backups actually make the RAID itself more secure. They do that by forcing all critical areas of the drives to be read continually, thus eliminating sleeper problems where an little used area of disk deteriorates and you only find it on a rebuild. When you do have a disk drive problem, you want to find it as quickly as possible. If you are relying on RAID alone, you run the risk of sleeper problems UNLESS you are using a scheduled RAID utility to regularly bad block the drives. Backups, of course, offer an additional value over that solution since they provide ... a backup of your data as well.
But having said that, ZFS type filesystems offer the ultimate solution in that they can detect and correct problems quickly without needing long rebuild times. However, there again, if your drives aren't being read on a regular basis as in regular complete backups, even ZFS type systems will risk sleeper problems where one or more clusters deteriorate and then the other drive fails leaving you sunk. I see a high level of risk with "lazy" disk drives. As with the human body, a little exercise pays huge dividends in the long run.
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