For storage only, you really shouldn't use RAID 0 or 1. Use RAID5 with 3 or more drives for some level of data redundancy, RAID6 for even more redundancy.
Using Mirror RAID as a backup strategy is just bad, as it actually increases your drive failure rate and doesn't protect against corruption issues - like sminlal said, you're better just having an "active" drive and a "backup" drive. Leave the backup drive offline, except when "backing up" data to it. It's really not the same as having a backup, because you're uninsulated against data corruption, but at least you have a second copy of your data somewhere if the active hard drive catches fire or something.