Fibre Channel part 1: FCP and WWPN addressing

SAN vocabulary first

A LUN (Logical Unit Number) is the “disk” presented to a host. It’s a SAN-only concept; there are no LUNs in NAS.

The initiator is the client. The target is the storage system.

Fibre Channel the protocol

The original SAN protocol, still everywhere. FCP carries SCSI commands over the FC network.

It’s completely separate from Ethernet at every OSI layer: dedicated HBAs (Host Bus Adapters), cables, and FC switches. Lossless by design, unlike Ethernet with TCP/UDP on top. Very stable, very reliable.

The speeds: 1, 2, 4, 8, 16, 32, 128 Gbps.

The network layout: clients reach the server over the normal Ethernet network, and the server reaches storage over the FC network through its HBA. Two parallel networks.

Addressing: World Wide Names

8-byte addresses, 16 hex digits: 15:00:00:f0:8c:08:95:de.

The WWNN (node name) is one per node and can cover several interfaces on that node. The WWPN (port name) is one per port, so a dual-port HBA carries two. Burned in by the manufacturer, globally unique: the Ethernet MAC analogy.

Config work cares about WWPNs, not WWNNs.

Aliases map friendly names to WWPNs (EXCHANGE-SERVER instead of 16 hex digits), configurable on both switches and storage. A big quality of life win for config and troubleshooting.

Continues in part 2: zoning and LUN masking.