June 05, 2015

vSphere Storage Terminologies - NPIV


With Fibre Channel (FC), nodes connect to each other via FC ports in order to exchange information. The following are some of the ports available on a FC network:
  • N_Port: This is a port on the Fibre Channel fabric. It is an end node port, used to connect a node to the fabric. This could be an HBA (Host Bus Adapter) in a server or a target port on a storage device.
    • N_Ports connect to the FC switch using an F_Port
  • F_Port: This is a port on a Fibre Channel switch that is connected to an N_Port. It is used to connect an N_Port point-to-point to a switch. This port makes use of the 24-bit port address.
    • F_Port is the port into which a server’s HBA or a storage array’s target port is connected
  • E_Port: This is an expansion (or extension) port. It connects switches. Switches connect to one another using an inter-switch link (ISL). The ports at the end of the ISL are E_Ports.
    • The connection between two E_Ports forms an Inter-Switch Link (ISL).
  • Other ports defined by the Fibre Channel protocol include the following and are less common:
    • FL_Port: fabric loop port
    • NL_Port: node loop port
    • L_Port: loop hub port
    • G_Port: generic port
    • U_Port: universal port
Once it is initialized and registered, an N_Port (an end node port) has the World-Wide Port Name (WWPN) of the physical HBA and is given an N_Port_ID. Each N_Port enables one connection to the FC fabric.

In a virtualization environment where multiple virtual machines can exist on a physical host with one or a small number of HBAs, there will be more virtual machines than N_Ports (or HBAs) to connect those virtual machines to the FC fabric.

N_Port_ID Virtualization (NPIV) enables the virtualization of WWPN and N_Port_ID. It is an ANSI T11 standard. It describes how a single FC physical HBA port can be registered on a fabric as multiple, virtual WWPNs. Using NPIV, an ESXi host for example may allow multiple virtual machines to connect to the SAN using just one or a few physical HBAs.

WWPN vs. N_Port_ID
Each FC HBA has both a world-wide node name (WWNN) and a world-wide port number (WWPN). The WWNN is a node name, i.e. it is used to identify the physical HBA on the server or the SAN switch chassis. The WWPN, which is more relevant in our discussion, uniquely identifies a port on a physical HBA. A dual-port HBA would have one WWNN and two WWPNs.

A world-wide port number (WWPN) is unique 64-bit identifier on each Fibre Channel port on a Fibre Channel device.

WWNN and WWPN are globally unique 64-bit addresses.
With the WWPN, a FC HBA port can register (Fabric Login (FLOGI)) with the switch and be given another FC address known as N_Port_ID.

The N_Port_ID is a 24-bit field used to route frames through a Fibre Channel network. The 24-bit field is composed of three bytes:
  • 1st byte (Domain ID):
    • This is the address of the FC switch or director
    • It is unique to the fabric
    • There are theoretically (256 – # reserved addresses) = 239 switches possible in a SAN fabric
  • 2nd byte (Area ID):
    • This part of the address is used to identify the individual switch ports
    • The Area ID is very similar to the 3rd byte
    • Identifies an N-type port that is connected to a switch
  • 3rd byte (Port ID)
    • This address is used to identify a single FC object on the SAN fabric
    • Provides 256 addresses for identifying attached N_Ports
N_Port_ID is a 24-bit address and it is used by the FC port for communication with the SAN.
The N_Port_ID is used for routing; the WWN/WWPN is used for both device level access control in a storage controller (LUN-masking) and for switch level access control on a FC switch (zoning).

With NPIV, a single physical HBA port can be assigned multiple virtual WWPNs.

In a SAN fabric each attached will be given a WWPN and an N_Port_ID.

  • N-Port ID Virtualization
  • An ANSI T11 standard
  • Describes how a single Fibre Channel Physical HBA port can register with a fabric using several worldwide port names (WWPNs), what might be considered Virtual WWNs
NPIV is available only for virtual machines with RDM disks, also the HBA and switch used to access the storage must be NPIV-capable.

"NPIV technology allows a single Fibre Channel HBA port to register with the Fibre Channel fabric using several worldwide port names (WWPNs). This ability makes the HBA port appear as multiple virtual ports, each having its own ID and virtual port name."


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