Emulex Computer Drive 355 User Manual
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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.
"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.
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.
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.
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