I've connected four different four TB drives in a RAID 5. This gives me 12TB to play with. I'm editing video with it. I know normally with hard drives you want to keep free space on drives. Do I need to do that with a RAID 5? Given the fact the combined space of the 4 drives is 16TB (although I only have 12TB to play with in the RAID 5 configuration), I wonder if the situation is different. So...do I need to leave free space?