However, if you plan a configuration that might be limited by the WWNN maximum, verify the  WWNN versus WWPN policy with the external storage vendor. Note:  Externally virtualized storage uses a separate capacity-based license. A tiered  capacity-based license varies depending on the drive technology that’s being virtualized  (this is known as  Storage Capacity Unit  (SCU) based licensing). IBM FlashSystem 9100 Models AF7 and AF8 support external virtualization. Use of the  external virtualization capability is entitled through the acquisition of IBM Spectrum Virtualize  Software for SAN Volume Controller (SW PID 5641-VC8 in AAS, and SW PID 5725-M19 in  IBM Passport Advantagefi).  External storage controllers with both types of attachment can be managed through the  External Storage pane. To access the External Storage pane, browse to  Pools External  Storage , as shown in Figure 5-62. The pane lists the external controllers that are connected to the FlashSystem 9100 system  and all the external MDisks detected by the system. The MDisks are organized by the  external storage system that presents them. You can toggle the sign to the left of the  controller icon to either show or hide the MDisks associated with the controller. Note:  A controller connected through Fibre Channel is detected automatically by the  system, providing that the cabling, the zoning, and the system layer are configured  correctly. A controller connected through iSCSI must be added to the system manually. If you have configured logical unit names on your external storage systems, it is not possible  for the system to determine this name because it is local to the external storage system.  However, you can use the external storage system WWNNs and the LU number to identify  each device. 158  IBM FlashSystem 9100 Architecture, Performance, and Implementation Figure 5-62 External Storage pane GLYPH<129> EMC DMX/SYMM, all HDS, and SUN/HP HDS clones use one WWNN per port.  Each port appears as a separate controller to the FlashSystem 9100. GLYPH<129> IBM, EMC CLARiiON, and HP  use one WWNN per subsystem. Each port appears  as a part of a subsystem with multiple ports, up to a maximum of 16 ports  (WWPNs) per WWNN. – The cluster can be connected to a maximum of 1024 WWNNs. The general customs  include the following practices: