General InformationI

Multi-Switch Fabrics

A Fibre Channel topology that consists of one or more interconnected switches or switch elements is called a fabric. Operational software provides the ability to interconnect switches (through expansion port (E_Port) connections) to form a multi-switch fabric. The data transmission path through the fabric is typically determined by fabric elements and is user-transparent. Subject to zoning restrictions, devices attached to any interconnected switch can communicate with each other through the fabric.

Because a multi-switch fabric is typically complex, maintenance personnel should be aware that several factors can degrade fabric performance or cause connectivity failures. These factors include:

•Domain ID assignment - Each switch in a fabric is identified by a unique domain ID that ranges from 1 through 31. A domain ID of 0 is invalid. If two operational fabrics join, they determine if any domain ID conflicts exist between the fabrics. If one or more conflicts exist, the E_Ports that form the interswitch link (ISL) segment to prevent the fabrics from joining.

•Zoning - In a multi-switch fabric, zoning is configured on a fabric-wide basis, and any change to the zoning configuration is applied to all switches in the fabric. To ensure zoning is consistent across a fabric, the following rules are enforced when two fabrics (zoned or unzoned) join:

—Fabric A unzoned and Fabric B unzoned - The fabrics join successfully, and the resulting fabric remains unzoned.

—Fabric A zoned and Fabric B unzoned - The fabrics join successfully, and fabric B automatically inherits the zoning configuration from fabric A.

—Fabric A unzoned and Fabric B zoned - The fabrics join successfully, and fabric A automatically inherits the zoning configuration from fabric B.

—Fabric A zoned and Fabric B zoned - The fabrics join successfully only if the zone configurations can be merged. If the fabrics cannot join, the connecting ports segment and the fabrics remain independent.

Zone configurations for two fabrics are compatible (the zones can join) if the active zone set name is identical for each fabric, and if zones with the same name have identical elements.

•Port segmentation - When an ISL activates, the switches exchange operating parameters to determine if they are compatible and can join to form a single fabric. If incompatible, the connecting E_Port at each switch segments to prevent