Designing The Fabric To Optimize Use Of Isl Trunking - HP StorageWorks MSA 2/8 - SAN Switch User Manual

Designing the Fabric to Optimize Use of ISL Trunking

ISL Trunking can be utilized to simplify SAN design and improve SAN
performance. When designing the SAN, consider the following recommendations
in addition to the standard guidelines for SAN design:
ISL Trunking Version 3.1.x/4.1.x User Guide
Evaluate the traffic patterns within the fabric. This allows implementation of
trunking groups that will help to optimize fabric performance. Refer to
"Evaluating Data Traffic
Place trunking-capable switches adjacent to each other. This maximizes the
number of trunking groups that can form.
Activate an ISL Trunking license on each switch that is expected to participate
in a trunking group.
The lengths of the ISLs in the group should differ by less than 30 meters
(recommended), and must differ by less than 400 meters. This is because large
differences in latency decrease the efficiency of load-sharing. If cable lengths
differ by 400 meters or more, the trunking group forms only for the ISLs that
have lengths that differ by less than 400 meters.
When connecting two switches with two or more ISLs, ensure that all
trunking requirements are met to allow a trunking group to form.
Determine the optimal number of trunking groups between each set of linked
switches, depending on traffic patterns and port availability. The goal is to
avoid traffic congestion without unnecessarily using ports that could be used
to attach other switches or devices.
Considerations:
— Each physical ISL uses two ports which could otherwise be used to attach
node devices or other switches.
— Trunking groups can be used to resolve ISL oversubscription if the total
capability of the trunking group is not exceeded.
If high data availability is the highest priority and there are enough ports
available, it is a good idea to set up redundant trunking groups with one or
two open ports in each trunk to allow for future expansion.
Consider how the addition of a new path will affect existing traffic patterns:
— A trunking group has the same link cost as the Master ISL of the group,
regardless of the number of ISLs in the group. This allows Subordinate
ISLs to be added or removed without causing data to be rerouted, since
the link cost remains constant.
Patterns" on page 29 for more information.
Setting Up ISL Trunking in a Fabric
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