FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availability Planning Guide (AA-RS2DC-TE, June 2003)

Planning Considerations for Fibre Channel Topologies
89SAN High Availability Planning Guide
Fabric Topologies
Several topologies exist from which to build a Fibre Channel fabric infrastructure.
This section describes the most effective fabric topologies, and provides guidance
on when to deploy each topology. The topologies are effective for a wide variety
of applications, are extensively tested by HP, and are deployed in several customer
environments.
Fabric topologies described in this section include:
■ Cascaded.
■ Ring.
■ Mesh.
■ Core-to-edge.
■ Fabric islands.
Cascaded Fabric
A cascaded fabric consists of a linear string of directors or switches connected by
one or more ISLs. Each fabric element is connected to the next fabric element in
line. The end-point fabric elements are not connected to each other. Figure 36
illustrates a cascaded fabric topology.
Cascaded fabrics are typically inexpensive, easy to deploy, and provide a simple
solution to add additional fabric devices. However, this fabric design has low
reliability because each director, switch, or ISL is a single point of failure. In
addition, the design has limited scalability because the maximum hop count can
be quickly exceeded when fabric elements are added.