vNUMA (Virtual NUMA) considerations
Non Uniform Memory Access also known as NUMA is designed with memory locality in mind so that pools of adjacent memory are placed in islands called NUMA nodes. Each of today's CPUs has multiple cores but that does not always result in a NUMA node with a given number of cores and RAM. It is the Integrated Memory Controller who decides that. There are multi-core CPU's that are not NUMA aware (original XEON 7300/7400 CPU's, for example), however on a different note, in a Nehalem-EX systems if it has four sockets each with 8 cores for a total of 32 cores and 256GB of RAM total, it would mean that each socket had 64GB of RAM.
What if your VM needs to be bigger than a NUMA node? One of the great new features in vSphere 5 is vNUMA or the ability for NUMA to be presented inside the VM to the guest OS.
vNUMA is designed for modern OS's that are NUMA aware and can make intelligent page management decisions based on locality.
Legacy OS functions in a similar manner...
