FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availability Planning Guide (AA-RS2DC-TE, June 2003)

Planning Considerations for Fibre Channel Topologies
70 SAN High Availability Planning Guide
Switched Mode Operation
When set to switched mode (default setting), a loop switch enables frame
transmission through multiple point-to-point connected pairs. Switched mode
operation and its simplified logical equivalent are illustrated in Figure 29.
Part (A) of Figure 29 shows server S
1
connected to device D
1
through a switched
pair of H_Ports, communicating at 1.0625 Gbps. Server S
2
is connected to device
D
2
through a second switched pair of H_Ports, also communicating at 1.0625
Gbps. Because of opportunistic bandwidth sharing, the two switched pairs
effectively increase the switch bandwidth to 2.125 Gbps. The remaining switch
H_Ports (four ports) are available for switched connection to each other, but
cannot communicate with servers S
1
and S
2
or devices D
1
and D
2
. Part (B) of
Figure 29 shows the logical equivalent of this arbitrated loop.
Figure 29: Switched mode operation and logical equivalent
Switched mode also allows independent operation of looplets of devices, each
connected through an unmanaged hub, and each attached to a single switch
H_Port. Figure 30 shows 8 hubs, each connected to a switch H_Port, and each
connected to a pair of devices (16 devices total). Each device pair forms a looplet
that communicates through a hub and connecting H_Port, and because of
opportunistic bandwidth sharing, the looplets effectively increase the switch
bandwidth to 8.5 Gbps.
H_Ports
D1 D2
D2S2S1
D1
S1 S2
A
B
Logical Equivalent
Loop Switch