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Cascading Switches
When multiple switches are connected, the connecting links between the switches are referred to
as "cascades". There are two distinct cascade configurations to consider when configuring
networks for optimal performance and connectivity: string cascades and tree cascades.
String Cascades
A string cascade connects multiple switches (up to three switches maximum) together in a "daisy-
chained" configuration. When one device requests access to another device, the request is sent to
each switch in the cascade before device access is granted. This arbitration method promotes
fairness between the switches. However, when compared to tree cascades, string cascades offer
less performance due to the increased latency between the switches.
When configuring a switch port for a string cascade, use the String Cascade Smart Setting. To
reduce contention and improve performance between initiator traffic and target traffic when using
a string cascade configuration, connect the ports of each switch together using the same String
Cascade Smart Settings. For example, in Figure 3-20 the three switches are connected through
two string cascades using the String Cascade - Trunk 1 and String Cascade - Trunk 2 Smart
Settings. This creates two dedicated paths through which initiators and targets can communicate.
Tree Cascades
Tree cascades provide the best performance (lowest latency) configuration. A tree cascade
consists of a root switch connected to additional switches (up to 8 switches maximum). When a
device on a switch requests access to another device, the request is sent the particular switch for
that device. The limitation to the tree cascade configuration is the random nature of devices
gaining access to one another, as fairness is not used for tree cascades.
When configuring a port for a tree cascade, use the Tree Cascade Smart Setting.
Figure 3-20: String Cascade configuration example
Figure 3-21: Tree Cascade configuration example
