HP Surestore 64 FW 05.01.00 and SW 07.01.00 HP StorageWorks SAN High Availabil - Page 71
Switched mode operation with eight independent looplets
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Planning Considerations for Fibre Channel Topologies Loop Switch H_Ports H_Ports Hub Hub Hub Hub Hub Hub Hub Hub S1 D1 S2 D2 S3 D3 S4 D4 S5 D5 S6 D6 S7 D7 S8 D8 Figure 30: Switched mode operation with eight independent looplets When communication within two or more looplets ceases, a device attached to one looplet can be switched to communicate with a device attached to another looplet. Downstream devices in a looplet are attached to an unmanaged hub; therefore, each looplet is operating in normal FC-AL loop mode. However, each looplet attaches to a switched H_Port and ideally should only support connections and operations for up to 32 FC-AL devices. Therefore, an arbitrated loop can be constructed that supports the architectural 125-device limit. Switched mode operation provides the ability to design a complex and high-performance SAN for the department or workgroup. Consider the following when planning such a SAN: ■ Connect loop switch H_Ports to multiple unmanaged hubs to provide additional FC-AL device connectivity in the form of looplets. Cascade the unmanaged hubs if more than eight hubs are necessary for the configuration. ■ Attach devices that frequently communicate with each other to the same looplet to take advantage of opportunistic bandwidth sharing (communication predominately stays within the loop). Switched connections through the loop switch allow connectivity as necessary to devices attached to other looplets. ■ Each looplet acts as a normal FC-AL loop. Spread multiple servers and high bandwidth storage devices across several looplets to avoid performance problems associated with a single looplet. SAN High Availability Planning Guide 71