The big problem I am seeing with the RS630 is what I'm going to do with these internal U.2 ports. The internal HBA that's connected to the backplane isn't the newer one that can run these, so these drives have to be direct-attached to their respective ports. U.2 drives get warm even though they're basically made of heat sink. I think my best option is to set them on top of the heat sinks at the back of the systems, which are cooling the 10GbE NIC and what I think is the motherboard chipset. If I do that, I won't have a place to stick a QDR Mellanox HBA for inter-server traffic.
If I set a couple U.2 drives in the back of the case, I'll probably 3D print some kind of retention bracket just to keep them from sliding around and to give some space for airflow around the heat sinks they'd otherwise be sitting on.
Lenovo offers
an inexpensive accessory HBA, the 1610-4P (there are also 8 port versions), allow mini-SAS connections to the backplane I *do* have, but according to Lenovo documentation, it's
only for single-CPU servers and only for the four backplane ports on the right-hand side of the system.
Nonetheless, this thing has an astonishing amount of I/O and it's not even a particularly new system.
(Yes, I know this isn't exactly "home NAS" but for as little as I paid for this thing, it could be).
Edit: Apparently I *do* have the right backplane. I just don't have all the cabling I should have for it. The joys of secondhand servers.