I have a Synology 2413+, that's a 12 bay NAS, and I think it's absolutely great, newest model is the 2419+, so mine is already a bit older. I also "only" have 4TB disks inside, and upgraded it from 2GB RAM to 4GB, but that's the max. So if I do stuff on it like archiving, what we guys do a lot, it's nowadays quite slow. But the 2419+ comes with 4GB and it's upgradable up to 32GB, so that's quite nice.
Running in RAID 6.
Although I don't host my ROMs on the NAS, but internally on PC plus USB HDD backup.