How is RAID1 not a substitute for file backup? It creates a complete redundant copy of data onto another drive, or more depending on how many drives you add to the RAID array. It's far easier than cherry picking files for individual backup, and you don't have the hours/days of downtime associated with having to reinstall everything.
RAID 0 gives you a boost in both read and write speed since the data is distributed amongst several drives, but you're fucked if one drive dies. RAID 1 sometimes takes a slight hit on write performance (depending on the controller) but usually gets faster read speeds, and if a drive dies, you still have X other copies of the drive on other drives so you can rebuild the array.
RAID is good for uptime, not backups, Backups give you protection against data loss or corruption
Edited:
RAID 5 god teir, RAID 6 is the only RAID that should even be considered "temp back up"