HP Tape Library Interface Manager Software - Manual (Page 29)

Chapter 2 Choosing the Right Configuration 29
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Fibre Channel Arbitrated Loop Addressing
On a FC arbitrated loop, 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 IM. The IM can be configured to use either
method.
Hard Addressing
Hard addressing is recommended for FC arbitrated loop 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.
When acquiring a hard address, the IM 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 IM will come up on the FC loop using an
available soft address. This allows the loop 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 IM.
When connected to a FC switch, the IM is identified to the switch as a unique
device by the factory programmed World Wide Name (WWN).
Soft Addressing
Soft addressing is recommended for FC fabric environments where the FC
interface card does not employ the Arbitrated Loop protocol. In these
environments, an AL_PA is not used as part of the device address, so soft
addressing allows the FC interface card to operate as an N_Port. Soft
addressing is recommended primarily for switched fabric configurations.
When acquiring a soft address, the FC interface card acquires the first
available loop address starting from address 01 and moving up the list of
available AL_PAs to EF. In this mode, the FC interface card 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 IM. FC
supports up to 126 devices on an arbitrated loop.