http://en.wikipedia.org/wiki/RAID

Raid 1 requires a minimum of 2 disks and protects against n-1 disk failures, not a 'single' disk failure, although it would protect against any 'single' disk failure even in it's minimum configuration. Raid 5 is the only selection available that never protects against more than a 'single' disk failure. More guessing games to try to figure out the author's meaning. Some authors are just being straightforward like this one and some seem to try to trick you with semantics. :w00t: