HP Surestore Tape Library Model 20/700 HP Surestore Bridge FC 2/1 LV and FC 4/ - Page 33

Chapter 2 Fibre Channel Arbitrated Loop Addressing On a Fibre Channel arbitrated loop (FC-AL), each device appears as an Arbitrated Loop Physical Address (AL_PA). To obtain an AL_PA, two methods called 'soft' and 'hard' addressing can be used by the bridge. The bridge can be configured to use either method. For hard addressing, the user specifies the AL_PA of the bridge. Hard addressing is recommended for FC-AL environments where it is important that the FC device addresses do not change. Device address changes can affect the mapping represented by the host operating system to the application. An example of such an environment would be a tape library installation, where the application configuration requires fixed device identification for proper operation. Hard addressing ensures that the device identification to the application remains constant. Hard Addressing When acquiring a hard address, the bridge attempts to acquire the AL_PA value that was specified by user configuration. If the desired address is not available at loop initialization time, the bridge comes up on the FC loop using an available soft address. This allows both the loop and the bridge to continue to operate. This situation would occur when another device on the arbitrated loop has acquired the same address as that configured on the bridge. When connected to a Fibre Channel switch, the bridge is identified to the switch as a unique device by the factory programmed World Wide Name (WWN). Soft Addressing When acquiring a soft address, the bridge acquires the first available loop address starting from address 01 and moving up the list of available AL_PAs from 01 to EF. In this mode, the bridge automatically obtains an available address and participates on the FC loop, as long as there is at least one address available on the loop that is connected to the bridge. Fibre Channel supports up to 126 devices on an arbitrated loop. Chapter 2 Fibre Channel Arbitrated Loop Addressing 35