HP StorageWorks 2/24 FW 07.00.00/HAFM SW 08.06.00 McDATA Products in a SAN Env - Page 90

Planning Considerations for Fibre Channel Topologies 3 Part (A) of Figure 3-1 shows device D1 connected to server S1 through a pair of H_Ports. Although the remaining switch H_Ports (six ports) and device D2 are unavailable for connection, frame traffic between device D1 and server S1 travels through a loop that consists of all eight H_Ports, device D1, device D2, and server S1. Each H_Port not participating in the communication pair and the NL_Port on device D2 provide a repeater function that allows frames to pass around the loop at the full switch bandwidth. Part (B) of Figure 3-1 shows the logical equivalent of this arbitrated loop. When frame transmission between device D1 and server S1 completes, the loop circuit closes and other ports attached to initiating devices arbitrate for loop access. When operating in shared mode, the switch is a serially reusable resource that provides service access to all ports on the loop. Access is granted by successful arbitration. When arbitration is won by a device, the loop is busy and other arbitrating devices must wait for loop access. Switched Mode Operation When set to switched mode, a switch bypasses full loop arbitration and enables frame transmission through multiple point-to-point connected pairs. Switched mode operation and its simplified logical equivalent are illustrated for a Sphereon 4500 Fabric Switch in Figure 3-2. Figure 3-2 Switched Mode Operation and Logical Equivalent 3-4 McDATA Products in a SAN Environment - Planning Manual