What type of RAM does a Xeon E5 v3 board need?

Registered DDR4 ECC (RDIMM) is what you need. Unbuffered sticks (UDIMM) are rare for this platform and often won’t work or will run at reduced performance. Most LGA 2011-3 boards are designed for RDIMMs, and the memory controller on the E5 v3 is built for registered memory’s extra buffering. Just buy PC4-2133 or 2400 registered ECC sticks off eBay.