Q-Logic 59021-05 B manual Common Topologies, Cascade Topology, 1. Cascade-with-a-Loop Topology

Q

3 – Planning Multiple Chassis Fabrics

3.2.2

Common Topologies

This section describes three commonly used topologies:

„Cascade

„Mesh

„Multistage®

3.2.2.1

Cascade Topology

A cascade topology describes a fabric in which the switches are connected in a linear fashion. If you connect the last switch back to the first switch, you create a cascade-with-a-loop topology as shown in Figure 3-1. The loop reduces latency because any switch can route traffic in the shortest direction to any switch in the loop. The loop also provides failover should a switch fail.

The cascade fabric shown in Figure 3-1has the following characteristics:

„Each chassis link contributes up to 200 MB/s of bandwidth between chassis, 400 MB/s in full duplex. However, because of the sequential structure, that bandwidth will be shared by traffic between devices on other chassis.

„Latency between any two ports is no more than three chassis hops.

„48 Fibre Channel ports are available for devices.

Figure 3-1. Cascade-with-a-Loop Topology

59021-05 B 3-3