Preferred path, Configuring a preferred path, Adding a preferred path – HP StorageWorks 2.64 Director Switch User Manual
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Optional features
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Preferred Path
The Preferred Path feature enables you to influence the route of data traffic when traversing more
than one Switch 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 source
port of the Switch or Director being configured, the exit port of that Switch or Director, and the
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.
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.