HP 316095-B21 - StorageWorks Edge Switch 2/24 Release Note page 19

When a Preferred Path is defined for all of the ports on a switch, it provides a
reasonable level of predictability because it isolates changes in routing only to the
ports affected by a particular "preferred path." Thus, if the "preferred path" goes
away, only the ports assigned to the path are rerouted to other paths. Conversely, if
the "preferred path" is re-established, the ports assigned to the path are rerouted
back to the path.
The Preferred Path enhancement modifies the behavior of Open Trunking by
providing guidance for the balancing function. The paths are balanced according
to the Open Trunking guidelines after the Preferred Path selections have been
assigned. Thus, the Preferred Path selections are eliminated from the list of
candidates to be moved off of a flow.
The Preferred Path configuration allows you to assign the exit port assignment,
but is subject to the standard rules regarding the FSPF protocol. Thus, if the
indicated path is not a least-cost route, the FSPF algorithm takes precedence.
Likewise, any port that does not have a Preferred Path definition is subject to the
static load-balance rules. And finally, a Preferred Path is not excluded from the
FSPF path selection operation for undefined or recovered paths.
Note:
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
such as OOOFs, but some devices send error messages. In FICON environments, an
IFCC error can result from an OOOF. To avoid these error messages, vary devices s
offline before a Preferred Path is activated, and then return the devices to online status
afterwards.
EWS enhancements
With firmware 06.00.00 and later, EWS enhancements include support for
managing the SANtegrity Binding feature and Enterprise Fabric Mode, and
providing the Link Incident (LIN) log and the Open Trunking log.
HP StorageWorks Edge Switch release notes
Activating a new Preferred Path will cause a reroute to occur if the Preferred Path
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