HP AA979A - StorageWorks SAN Switch 2/8V, Administrator'S Manual, Page: 351 / 465

Fabric OS 5.3.0 administrator guide 359
19 Administering ISL Trunking
This chapter contains procedures for using the ISL Trunking licensed feature, which optimizes the use of
bandwidth by allowing a group of interswitch links to merge into a single logical link.
Overview
ISL Trunking reduces or eliminates situations that require static traffic routes and individual ISL management
to achieve optimal performance. Trunking optimizes fabric performance by distributing traffic across the
shared bandwidth of all the interswitch links in a trunking group, allowing traffic to flow through any
available link in a group rather than restricting it to a specific, potentially congested link. The use of
trunking results in simplified fabric design and management, lowered cost of ownership, and increased
data availability.
To use trunking, you must first install the ISL Trunking license. For details on obtaining and installing
licensed features, refer to ” Maintaining licensed software features ” on page 36. Trunking is enabled
automatically when the ISL Trunking license is activated and ports are reinitialized (after installing the
license, you enter the
switchDisable
and
switchEnable
commands), and trunks are easily
managed using either Fabric OS CLI commands or Web Tools. You can enable and disable trunking and
set trunk port speeds (for example, 2 Gig/sec, 4 Gig/sec, or autonegotiate) for entire switches or for
individual ports.
Trunks distribute traffic dynamically and in order at the frame level, achieving greater performance with
fewer interswitch links.
Trunks are compatible with both short wavelength (SWL) and long wavelength (LWL) fiber optic cables and
transceivers.
Figure 22 illustrates how trunking can result in more throughput by distributing data over four ISLs with no
congestion. In a fabric that does not have trunking capability, some paths would be congested and other
paths underutilized.
Figure 22 Distribution of traffic over ISL Trunking groups
Trunks operate best when the cable length of each trunked link is roughly equal to the others in the trunk.
For optimal performance, no more than 30 meters difference is recommended.