I would suggest reading up first on what RAID is exactly and how to make yourself a suitable backup plan.
RAID 1 mirrors the contents of the disks, making a form of 1:1 ratio realtime backup. The contents of each disk in the array are identical to that of every other disk in the array. A RAID 1 array requires a minimum of two drives. RAID 1 mirrors, though during the writing process copy the data identically to both drives, would not be suitable as a permanent backup solution, as RAID technology by design allows for certain failures to take place.
Please note:
RAID 1 mirrors, though during the writing process copy the data identically to both drives, would not be suitable as a permanent backup solution, as RAID technology by design allows for certain failures to take place.
http://en.wikipedia.org/wiki/RAID#RAID_1