HP StorageWorks Fabric OS 6.2 administrator guide (5697-0016, May 2009)

Fabric OS 6.2 administrator guide 437
• Trunking groups can be used to resolve ISL oversubscription if the total capability of the trunking
group is not exceeded.
• 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 slave ISLs to be added or removed without causing data to be
rerouted, because the link cost remains constant.
• The addition of a path that is shorter than existing paths causes traffic to be rerouted through that
path.
• The addition of a path that is longer than existing paths may not be useful because the traffic will
choose the shorter paths first.
• Plan for future bandwidth addition to accommodate increased traffic.
For trunking groups over which traffic is likely to increase as business requirements grow, consider
leaving one or two ports in the group available for future nondisruptive addition of bandwidth.
• Consider creating redundant trunking groups where additional ports are available or paths are
particularly critical.
This helps to protect against oversubscription of trunking groups, multiple ISL failures in the same group,
and the rare occurrence of an ASIC failure.
• To provide the highest level of reliability, deploy trunking groups in redundant fabrics to further ensure
that ISL failures do not disrupt business operations.
Initializing trunking on ports
After you unlock the ISL Trunking license, you must reinitialize the ports being used for ISLs so that they
recognize that trunking is enabled. This procedure needs to be performed only once.
To reinitialize the ports, you can either disable and then re-enable the switch, or disable and then
re-enable the affected ports.
1. Connect to the switch and log in using an account assigned to the admin role.
2. Enter the switchDisable command.
3. Enter the switchEnable command.
Disabling and re-enabling ports
1. Connect to the switch and log in using an account assigned to the admin role.
2. Enter the portDisable command. The format is:
portDisable [slot/]port
On directors and enterprise-class platforms, slot is the slot number and port is the port number of
the port you want to disable.
3. Enter the portEnable command.The format is:
portEnable [slot/]port
On directors and enterprise-class platforms, slot is the slot number and port is the port number of
the port you want to enable.
Lossless Dynamic load sharing on trunk ports
Lossless Dynamic Load Sharing (DLS) allows you to rebalance trunk port paths without causing
input/output (I/O) failures in cases where the end devices require in-order-delivery (IOD) of frames. You
can use this feature with the HP StorageWorks 8/40 SAN Switch, HP StorageWorks 8/80 SAN Switch, HP
StorageWorks DC SAN Backbone Director, and the HP StorageWorks DC04 SAN Director Switch
platforms.
You can use DLS on trunks connecting switches to perform the following functions:
• Eliminate dropped frames and I/O failures by rebalancing the paths going over the ISLs whenever
there is a fabric event that might result in sub-optimal utilization of the ISLs.
• Eliminate the delay caused by establishing a new path when a topology change occurs.
• Pause ingress traffic (by not returning credits).