I have 2 new 640GB WD drive. And I have a box for 3 drives. I put one of them in the 1. slot and the other into the 3. slot. In the 1. slot is the HDD upside down and so there is ~1cm place from the box top sidewall. However if I place it normally into the 1. slot then there will be a 1mm(!) place between the HDD and the box top sidewall and it seems to be not the best as no airflow there.
I have the following possibilities:
1. 1mm space - HDD - 4cm space - HDD - 1cm space
2. 1cm space - HDD (upside down) - 3cm space - HDD - 1cm space
3. 3,5cm space - HDD (slot 2) - 0,5cm space - HDD - 1cm space