Compaq StorageWorks HSG60 ACS Solution Software V8.6 for Sun Solaris Installation and Configuration Guide

Fibre Channel: Considerations for Both Loop and Fabric Environments 6–5
You can extend the fabric’s capability by adding more subsystems, more switches, or more
servers. Adding switches is probably the easiest. To add a switch, all that must be done is
to connect it to the existing fabric.
In a fabric configuration of cascaded switches, there is only one principal switch. If there
are two separate switch configurations there will be two principal switches and care must
be taken when integrating the two switch configurations.
The most common problem encountered when adding a switch to the fabric is domain
overlap, especially when interconnecting old (Compaq Fibre Channel) and new (Compaq
SAN) switches. Every switch in a domain must have a unique domain ID. Refer to the
documentation that came with your switch for more information on changing domain IDs
and cascading switches.
To connect a server or a switch to another switch, insert the Fibre Channel cables are
inserted into the gigabit interface converters (GBICs) that reside in each port of the switch.
In summary, connections between switches are similar to connections between server and
switch with the added ability of adding more switching capability and/or more storage.
The Fibre Channel Access/Transport Paths
In a fibre loop, a server’s target is specified by the controller’s port(s). These ports have
physical addresses (PA) and in a loop that is arbitrated, the ports are called arbitrated loop,
physical addresses (ALPAs). Since all servers and storage systems connected to a loop
share PA, it is important that every port on the loop have a unique ALPA.
In the fibre fabric the basic target is the controller’s Worldwide Node Name (WWNN).
The WWNN is the fabric network address for the controller of the RAID array. WWNNs
have a format of AAAA-BBBB-CCCC-DDDD, where A, B, C, D are alphanumeric
characters.
Each controller has two ports and each port has a designated Worldwide Port Name
(WWPN). In the StorageWorks’ Sun implementation, the specific WWPNs are used to
define what nodes in the fabric that Sun will attempt to bind to. (See “Worldwide Names
(Node IDs and Port IDs),” page 1–26 for details.)
In summary, Compaq manages two entities with Fibre Channel: ALPAs for loop and
WWPNs for fabric.