Fibre Channel SAN Configuration Guide : Managing ESX Server Systems That Use SAN Storage : N-Port ID Virtualization : Requirements for Using NPIV

Requirements for Using NPIV
Before you attempt to implement NPIV by assigning WWNs to your virtual machines, be aware of the following requirements and limitations:
NPIV can only be used for virtual machines with RDM disks. Virtual machines with regular virtual disks use the WWNs of the host’s physical HBAs. For more information on RDMs, see the ESX Server 3 Configuration Guide or ESX Server 3i Configuration Guide.
For this implementation of NPIV, the physical HBAs on an ESX Server host, using their own WWNs, must have access to all LUNs that are to be accessed by virtual machines running on that host.
QLogic – any 4GB HBA.
Emulex – 4GB HBAs that have NPIV-compatible firmware.
When configuring an NPIV LUN for access at the storage level, make sure that the NPIV LUN number and NPIV target ID match the physical LUN and Target ID.