HP StorageWorks 2/140 FW 08.01.00 McDATA Products in a SAN Environment Plannin - Page 107

Planning Considerations for Fibre Channel Topologies 3 When balancing a load across multiple ISLs, a director or switch attempts to avoid assigning multiple ports attached to a device to the same ISL. This minimizes the probability that failure of a single ISL will affect all paths to the device. However, because port assignments are made incrementally as devices log into the fabric and ISLs become available, optimal results are not guaranteed. Special consideration must also be given to applications with high data transfer rates or devices that participate in frequent or critical data transfer operations. For example, in Figure 3-11, suppose device D7 is a server and device D9 is a storage unit and both devices participate in a critical nightly backup operation. It is recommended that such a connection be routed directly through director S2 (rather than the entire fabric) through zoned port connections, WWN-bound port connections, or a preferred path. For additional information, refer to Device Locality. • Zoning - For multiswitch fabrics, zoning is configured on a fabric-wide basis. Changes to the zoning configuration apply to all directors and switches in the fabric. To ensure the zoning configuration is maintained, certain rules are enforced when two or more elements are connected through ISLs to form a fabric or when two or more fabrics are joined. For additional information, refer to Configuring Zones. After directors and fabric switches are defined and cabled, they automatically join to form a single fabric through a user-transparent process. However, the user should be aware of the following fabric concepts, configuration characteristics, and operational characteristics: • Principal switch selection - Setting this value determines the principal switch for the multiswitch fabric. Select either Principal (highest priority), Default, or Never Principal (lowest priority) from the Switch Priority drop-down list. If all fabric elements are set to Principal or Default, the director or fabric switch with the highest priority and the lowest WWN becomes the principal switch. Following are some examples of principal switch selection when fabric elements have these settings. - If you have three fabric elements and set all to Default, the director or switch with the lowest WWN becomes the principal switch. Planning Considerations for Fibre Channel Topologies 3-23