General thought is to split the cameras on both drives.
Then say you have 4 cameras on the front, 4 on the back, 4 on the left side of the house, and 4 on the right side of the house - take those 16 cameras and put 2 from each side on one drive and 2 from each side on the other drive so that if one drive goes out, you still have coverage on all the sides.
Then say you have 4 cameras on the front, 4 on the back, 4 on the left side of the house, and 4 on the right side of the house - take those 16 cameras and put 2 from each side on one drive and 2 from each side on the other drive so that if one drive goes out, you still have coverage on all the sides.