McDATA StorageWorks 2/140 - Director Switch Planning Manual page 106

Planning Considerations for Fibre Channel Topologies
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McDATA Products in a SAN Environment - Planning Manual
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• Bandwidth - ISL connections can be used to increase the total
bandwidth available for data transfer between two directors or
switches in a fabric. Increasing the number of ISLs between
elements increases the corresponding total ISL bandwidth but
decreases the number of port connections available to devices.
• Load balancing - Planning consideration must be given to the
amount of data traffic expected through the fabric or through a
fabric element. Because the fabric automatically determines and
uses the least cost (shortest) data transfer path between source
and destination ports, some ISL connections may provide
insufficient bandwidth while the bandwidth of other connections
is unused.
To optimize bandwidth use and automatically provide dynamic
load balancing across multiple ISLs, consider purchasing and
enabling the OpenTrunking feature key. For information about
the feature and managing multiple ISLs, refer to
and General Fabric Design
• Preferred path - Preferred path is an option that allows a user to
configure an ISL data path between multiple fabric elements
(directors and fabric switches) by configuring the source and exit
ports of the origination fabric element and the Domain_ID of the
destination fabric element. Each participating director or switch
must be configured as part of a desired path. For information
about the feature, refer to
ATTENTION ! Activating a preferred path can result in receipt of out-of-
order frames if the preferred path differs from the current path, if input and
output (I/O) is active from the source port, and if congestion is present on the
current path.
In general, Fibre Channel frames are routed through fabric paths
that implement the minimum possible hop count. For example, in
Figure 3-11, all traffic between devices connected to director S
and director S communicate directly through ISLs that connect
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the directors (one hop). No traffic is routed through director S
(two hops). If heavy traffic between the devices is expected,
multiple ISL connections should be configured to create multiple
minimum-hop paths. With multiple paths, the directors balance
the load by assigning traffic from different ports to different
minimum-hop paths (ISLs).
Considerations.
Preferred Path.
OpenTrunking
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