ann.... RAID 1.5 may not be the best choice now. (check out Tom's hardward guide)
To optimun video processing, I would recommand any RAID-0 configuration. Like tachibana describes there is a potential threat of losing datas for this type of configuration. The best way to get around with this issue is to have the system file stroed in another hdd. (which will require at least 3 hdds)
money...money.....$_$..... I want money....