Not a backup, but depending on the RAID type it'll allow you to recover from the loss of a drive or two.
Is this data loss?
Repeat after me, RAID is not a backup
RAID is not a backup
RAID is not a backup
Said it twice so it doesn't get lost
RAID… is… a backup!
The only good back up is the binary carved in to stone tablets.
Not a backup, but depending on the RAID type it'll allow you to recover from the loss of a drive or two.