It’s just 3D printed plastic. There isn’t any backplane or anything. You hook up the drives yourself with SATA power and data cables to the PSU and whatever ports you want to use on the motherboard or an HBA. It screws into the back of the case above the IO shield, so can block airflow. It can also be a bit tricky if you actually want to use all six to get the cables attached since the spacing is pretty tight, so you need to alternate with half the ports on the left and half on the right or something. There are other designs floating about that have the drives aligned parallel to the airflow rather than perpendicular to it, or ones for only two drives if you don’t need six. The main issue is probably cabling the power.
https://forum.45homelab.com/t/6bay-ssd-bracket-kit/3512/12
Most A310s I am aware of are 15-17 cm in length. So, yeah.
Sorry, I’m going to use Freedom Units. (The HL15 is 20 inches deep not including the thumbscrews that protrude at the front). I would think an additional 3 to 4 inches at the back would be sufficient. The I/O area and PCIe slots are recessed slightly, maybe an additional half inch. There are feet included to stand the case on it’s side if that is an option for your space. Are you looking at closed or open racks? With a tight space the power button is going to be on the back, so keep that in mind, you might be using mostly the BMC to power the server on and off.