FW V06.XX/HAFM SW V08.02.00 HP StorageWorks SAN High Availability Planning Guide (AA-RS2DD-TE, July 2004)

Planning Considerations for Fibre Channel Topologies
76 SAN High Availability Planning Guide
The switch B_Port provides a single 1.0625 Gbps ISL to an E_Port on a director
or edge switch. Direct ISL connectivity between loop switches (with or without a
redundant B_Port connection to a director or edge switch) is generally not
supported. However, a director or edge switch does support the connection of
multiple, independent switches. Figure 31 shows a configuration of two loop
switches attached to a director.
Figure 31: Arbitrated loop to switched fabric connectivity
Consider the following when planning arbitrated loop-to-switched fabric
connectivity and incorporating FC-AL devices into the enterprise SAN
environment:
■ B_Port traffic is routed through a user-transparent FL_Port that is embedded
on the switch’s control processor (CTP) card. Switch mode (shared or
switched) has no impact on B_Port operation. However, because all
switch-attached FC-AL devices must arbitrate for access to the embedded
FL_Port, loop performance issues (loop round-trip time, number of loop
tenancies, service rate, and loop utilization) must be evaluated.
■ Although the B_Port connection (ISL) between the director and switch is a
1.0625 Gbps serial connection, burst transmissions from multiple FC-AL
devices are multiplexed and buffered (the link BB_Credit value is eight) and
may coexist in the link. Therefore, the sum of the bandwidths of all devices
contending for B_Port access should not exceed 1.0625 Gbps. Exceeding the
total bandwidth may result in degraded performance, as shown in Figure 32.