Registered ECC (RDIMM) vs unbuffered ECC (UDIMM): RDIMM is the right call for Xeon E5 v3 boards

Your Xeon E5 v3 board expects registered DDR4 ECC, not unbuffered. UDIMMs are rare for this platform and often won’t work or will run at reduced performance, while RDIMMs are cheap and plentiful on eBay. Most LGA 2011-3 boards are designed for RDIMMs’ extra buffering, especially with multiple ranks and higher capacities.