This is a great script to keep handy. If you have multiple RDM’s on a VM and need to get the NAA_ID for them the below PowerCLI command will get you that information.
Get-VM VMNAME| Get-HardDisk -DiskType "RawPhysical","RawVirtual" | Select Parent,Name,DiskType,ScsiCanonicalName,DeviceName,CapacityGB | fl If you then need to match the SCSI virtual disk to the Guest OS this is a great article on how to do so.
KB2051606