NPIV or N-Port Virtualization is a method of utilizing a single Fibre Channel port to serve multiple physical or virtual servers. NPIV allows a single SAN device to service multiple WWNs without additional switching infrastructure. NPIV is the technique used by blade system hardware to reduce the complexity of SAN connected blades. NPIV allows SAN connectivity without requiring Fibre Channel switches to be installed within the blade chassis. VMware also uses NPIV within the Raw Device Mapping (RDM) infrastructure.
Due to a statement in VMware documentation, confusion has arisen over support of Microsoft Cluster Server (MSCS) in a VMware environment where NPIV is utilized. In short NPIV is supported with VMware and MSCS where a hardware device such as HP Virtual Connect or Cisco UCS provides the NPIV functionality but not where VMware is providing the NPIV (checking the box in the guest config of a VM for NPIV).
