0 - 2 of 2 tags for fallback

Tables with fallback protection ensures that copy of each row is available on fallback AMPs in the same CLUSTER. I have few questions on this.
1) How do i identify that what all AMPs are the part of same cluster. 
2) Is there any console utility in teradata to check the AMPs which are grouped together?

  What is the need for having FALLBACK option during creating Tables when we have RAID-1 which has a mirror copy of a disk.doesnt it add overhead and cost?