http://forums.cnet.com/7726-7588_102-5554028.html?tag=posts;msg5554028

The problem is simply that we can't trust any of these explicitly. We continue to need one more to be sure to have a backup copy. Your IT schooling teaches you that you get 3. That way when one fails, you are still in a state of backup. When we have one lone copy, danger looms.
Bob