HP Surestore 64 Planning Guide - Page 91

Table 2 ISL Transfer Rate Versus Fabric Port Availability (Two-Director Fabric) Number of ISLs ISL Data Transfer Rate Available Fabric Ports 1 1.0625 Gbps 126 2 2.1250 Gbps 124 3 3.1875 Gbps 122 4 4.2500 Gbps 120 5 5.3125 Gbps 118 6 6.3750 Gbps 116 7 7.4375 Gbps 114 8 8.5000 Gbps 112 • Load balancing Planning consideration must be given to the amount of data traffic expected through the fabric. 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. Fibre Channel frames are routed through fabric paths that implement the minimum possible hop count. For example, in Figure 19, all traffic between devices connected to director S1 and director S2 communicate 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, the director 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. Planning Considerations Multiswitch Fabric Support 77