HP Surestore 64 FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availabil - Page 82

Planning Considerations for Fibre Channel Topologies Table 2: ISL Transfer Rate versus Fabric Port Availability (Two-Director Fabric) Number of ISLs 1 2 3 4 5 6 7 8 ISL Data Transfer Rate (at 1.0625 Gbps) 1.0625 Gbps 2.1250 Gbps 3.1875 Gbps 4.2500 Gbps 5.3125 Gbps 6.3750 Gbps 7.4375 Gbps 8.5000 Gbps ISL Data Transfer Rate (at 2.125 Gbps) 2.1250 Gbps 4.2500 Gbps 6.3750 Gbps 8.5000 Gbps 10.6250 Gbps 12.7500 Gbps 14.8750 Gbps 17.0000 Gbps Available Fabric Ports 126 124 122 120 118 116 114 112 ■ 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. For additional information, refer to "Large Fabric Design Implications" on page 107. Fibre Channel frames are routed through fabric paths that implement the minimum possible hop count. For example, in Figure 35 on page 78, all traffic between devices connected to Director S1 and Director S2 communicates directly through ISLs that connect the directors (one hop). No traffic is routed through Director S3 (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). 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. 82 SAN High Availability Planning Guide