The Define One has support for 6x 2.5" drives or 2x 3.5" drives and 2x 2.5" drives. The case has 2x 2.5"/3.5" mounts on the backside of the motherboard plate, and 2x dedicated 2.5" mounts in the bottom.
(There are clips in the bottom which you just push the 2.5" drive into)
If you are using a rear connector motherboard, you can move the rear motherboard plate mounts to the left to accommodate the rear motherboard connectors, as shown below:
This would however require that you move the cable mounts to alternate positions than the pre-installed. See below for locations these can be put:
