HDVR2 WITH TWO DRIVES

I have the opportunity to acquire a working HDVR2 that has two 120Gb drives. I have the following questions:
Are the two drives Identical?
If yes, does this mean I can remove one drive if I want to?
If yes, can I put that removed drive into another HDVR2 to replace a defective drive?
If no, does it mean that if either drive fails the unit fails too?

Thank you

HDVR2 WITH TWO DRIVES