Both drives fail at the same time, but mechanical failure are usually the fault of one drive and not both. Only file system errors carry through both streams. I've had an array fail a while back with those crappya55 maxtor drives. 1 had a mechanical problem and I had to recover using array building software. Winternals does a good job.......Its a hassle but recovery from raid drives is not impossible......
By the way....that was the last time I was a customer of the maxtor corporation.