FW 05.01.00 and SW 07.01.00 HP StorageWorks Embedded Web Server User Guide (AA-RTDRB-TE, June 2003)

Configuring the Product
49Embedded Web Server User Guide
Configuring Open Trunking
The Open Trunking page enables you to configure open trunking settings. Open
Trunking is an optional software feature that is enabled using a feature key.
The purpose of Open Trunking is to make efficient use of redundant interswitch
links (ISLs) between neighboring switches by means of load balancing. ISLs are
fiber optic cables that connect ports between Fibre Channel switches and link
these switches into a multiswitch fabric. Fibre Channel traffic flows through these
ISLs from end devices (servers and storage devices) attached to ports on
individual switches.
When the traffic on a particular port exceeds a specified threshold, the Open
Trunking functionality routes some of the traffic to another ISL. This prevents
traffic from becoming congested on an ISL. Open trunking provides automatic,
dynamic, statistical traffic load balancing across ISLs in a fabric environment.
The Open Trunking feature monitors Fibre Channel data rates through multiple
ISLs, dynamically applies a fibre shortest path first (FSPF) networking algorithm
to calculate the optimum path between fabric elements, and balances the Fibre
Channel traffic load accordingly. The objective is to make the most efficient
possible use of redundant ISLs between neighboring switches, even if these ISLs
have different bandwidths.
The Open Trunking feature monitors the average data rates of all traffic flows
(from a transmit port to a destination domain), and periodically adjusts routing
tables to reroute data flows from congested links to lightly loaded links and
optimizes bandwidth use.
Load-balancing among the ISLs does not require user configuration, other than
enabling open trunking and selecting optional or default settings for congestion
thresholds (per port) and a response threshold for lack of BB_Credits. In
particular, you do not need to manually configure ISLs into trunk groups of
redundant links where data can be off-loaded.
Candidate links for rerouting flow are identified automatically and maintained by
the FSPF protocol. All ISLs that lead to adjacent switches on the shortest path to
the flow’s destination are considered. This means that even if a link is not on the
shortest path to the destination, the flow may be rerouted to this link to relieve
congestion. This also means that flow may be rerouted onto a link that goes to a
different adjacent switch.