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Addressing, Structures and Operation D-3
D-
Addressing, Structures and Operation
Fibre Channel and SCSI systems employ different methods of
addressing devices. The inclusion of a bridge or router
requires that a method of translating device IDs be
implemented so that each SCSI device is mapped to the
appropriate Fibre Channel LUN. The SCSI buses establish bus
connections between devices. Targets on a SCSI bus may
internally address logical units. The addressing of a specific
SCSI device is represented by the BUS:TARGET:LUN triplet.
When a Fibre Channel initiator initializes on an arbitrated
loop, the first order of business is to determine what devices
exist on the loop. Device discovery is performed, and an FCP
target device list is built. Each device is queried for FCP logical
units. The logical units are the actual devices that the
operating system will address. When an initiator addresses a
logical unit, the LUN field used is consistent in form with the
SCC defined fields. All current Fibre Channel host bus
adapter drivers are consistent with these methods. The
addressing used is the SCC Logical Unit Addressing and
Peripheral Device Addressing methods, shown in Table D-1
and Table D-2. First level addressing is supported, so only the
first 2 bytes of the 8 byte FCP LUN are used.
Table D-1 SCC Addressing Structure
Bits
Bytes
76543210
n Address Method Address Method Specific
n+1 Address method Specific
Table D-2 Peripheral Device Addressing LUN Structure
Bits
Bytes
76543210
n 0 0 Bus
n+1 Target/LUN