HP StorageWorks 2.140 Director Switch - Manual (Page 128)

Configuring the Director
126 Director Element Manager User Guide
Configuring a Preferred Path
The Preferred Path feature enables you to influence the route of data traffic when
traversing multiple switches or directors in a fabric. If more than one ISL connects
switches in your SAN, this feature will be useful for specifying an ISL preference
for a particular flow. The data path consists of the following:
■ Source port of the switch or director being configured
■ Exit port of that switch or director
■ Domain ID of the destination switch or director.
Each switch or director must be configured for its part of the desired path in order
to achieve optimal performance. You may need to configure Preferred Paths for all
switches or directors along the desired path for proper multi-hop Preferred Path
operation. The following is an example of the procedure to use.
Adding a Preferred Path
To add a new preferred path, use the following steps:
Caution: Activation of a new Preferred Path will cause a reroute to occur if the
Preferred Path is different from the current path. In congested environments,
with traffic on the current path, a reroute can cause an out of order frame
(OOOF) at the destination device.
Reroutes are a natural activity in any Fibre Channel fabric when the network is
modified. For example, reroutes occur when ISLs are added or lost or when
new switches are added to the fabric. Fibre Channel devices are designed to
handle errors like OOOFs, but some send error messages when they occur.
In FICON environments, an IFCC error can result from an OOOF. To avoid
these error messages, devices should be varied offline before a Preferred Path
is activated, and returned to online status after the activation.
1. Click Configure > Preferred Path. The Configure Preferred Paths dialog box
displays as shown in Figure 34 . The Configure Preferred Paths dialog box
provides the configuration for a single switch’s preferred path.