HP Surestore 64 FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availabil - Page 68
Device private arbitrated loop, hub. Server S
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Planning Considerations for Fibre Channel Topologies Hubs are cascaded through H_Port-to-H_Port connections (one port per switch or hub). Server S1 communicates with device D1 through a loop that includes H_Ports on all three hubs and NL_Ports on the remaining 18 devices. Loop Switch Loop Switch H_Ports Hub H_Ports Hub S1 D1 Figure 28: 20-Device private arbitrated loop Although connection of additional devices to a loop does not impact switch bandwidth (1.0625 Gbps), it does adversely impact overall loop performance because part of the bandwidth is dedicated to overhead instead of information transmission. Loop performance is a complex function of several factors, including the: ■ Loop round-trip time - The time required for a frame to travel completely around a loop is a function of the propagation delay associated with each H_Port and NL_Port, and the time required to travel through the fiber-optic or copper transmission medium. The addition of ports (through cascaded hubs), devices, and cabling increases the round-trip time. 68 SAN High Availability Planning Guide