6.5.1

Generally, a single path from a host to a LUN consists of an HBA, switch ports, connecting cables, and
the storage controller port. If any component of the path fails, the host selects another available path for
I/O. The process of detecting a failed path and switching to another is called path failover.
Ports in Fibre Channel SAN
In the context of this document, a port is the connection from a device into the SAN. Each node in the
SAN, such as a host, a storage device, or a fabric component has one or more ports that connect it to the
SAN. Ports are identified in a number of ways.
WWPN (World Wide
Port Name)
A globally unique identifier for a port that allows certain applications to
access the port. The FC switches discover the WWPN of a device or host
and assign a port address to the device.
Port_ID (or port
address)
Within a SAN, each port has a unique port ID that serves as the FC
address for the port. This unique ID enables routing of data through the
SAN to that port. The FC switches assign the port ID when the device logs
in to the fabric. The port ID is valid only while the device is logged on.
When N-Port ID Virtualization (NPIV) is used, a single FC HBA port (N-port) can register with the fabric by
using several WWPNs. This method allows an N-port to claim multiple fabric addresses, each of which
appears as a unique entity. When ESXi hosts use a SAN, these multiple, unique identifiers allow the
assignment of WWNs to individual virtual machines as part of their configuration.
Fibre Channel Storage Array Types
ESXi supports different storage systems and arrays.
The types of storage that your host supports include active-active, active-passive, and ALUA-compliant.
Active-active storage
system
Supports access to the LUNs simultaneously through all the storage ports
that are available without significant performance degradation. All the paths
are active, unless a path fails.
Active-passive storage
system
A system in which one storage processor is actively providing access to a
given LUN. The other processors act as a backup for the LUN and can be
actively providing access to other LUN I/O. I/O can be successfully sent
only to an active port for a given LUN. If access through the active storage
port fails, one of the passive storage processors can be activated by the
servers accessing it.
Asymmetrical storage
system
Supports Asymmetric Logical Unit Access (ALUA). ALUA-compliant storage
systems provide different levels of access per port. With ALUA, the host
can determine the states of target ports and prioritize paths. The host uses
some of the active paths as primary, and uses others as secondary.
vSphere Storage
VMware, Inc. 38