The problem is the DL980 has a problem. HP knows the Nehalem EX does not scale well past 4 sockets because there are only 4 QPI links on the chip so they created a XNC (cross-network connector) to be similar to IBM's eX5 architecture. Unfortunately it is HP's first try at a "glue" chip for Xeon and it does not work very well. They also only have I/O connected to some of the CPU's as it is a top and bottom drawer config. The 128 DIMM slots are also causing heat issues as they are in front of the processors and the heat off the memory can do wacky things to the Nehalems.
There is no redundant clock, redundant fabric or service processor, no double-chip spare, or rundant address control pins on the dimm, so you will need two clustered together.