if you are doing this for real- you need to follow the advice of the real hd video pro's

the decklink support pages have some hints:

http://decklink.com/support/detail.asp?techID=62

Recommended disks for building HD disk arrays are currently the Seagate Cheetah Ultra-320 10k.6, Ultra-320 15k.2 or the Maxtor Ultra-320 10k drives. We don't recommend Ultra-160 drives for uncompressed HDTV work.

We recommend 8 x 10k drives or 6 x 15k drives when building an array. However, you can go as low as 6 for 10k and 4 for 15k; however the extra disks will help improve performance as the drives fill to capacity.