Virtual TapeServer SCSI-to-FC Adapter User Manual

C-1
Appendix C
Addressing, Structures, and Operation
Fibre Channel and SCSI systems employ different methods of addressing devices. The inclusion of
a VT5900-SA 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 a loop, the host must first 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 C-1 and Table C-2. First level addressing
is supported, so only the first 2 bytes of the 8 byte FCP LUN are used.
Table C-1. SCC Addressing Structure
Table C-2. Address Method Definitions
Table C-3. SCC Logical Unit Addressing
Bit
Byte
7 6 5 4 3 2 1 0
N Address
Method
Address Method Specific
N+1
Address Method Specific
Codes Description
00 Peripheral Device Addressing Method
01 Volume Set Addressing Method
10 Logical Unit Addressing Method
11 Reserved
Bit
Byte
7 6 5 4 3 2 1 0
N 1 0 Target
N+1 Bus LUN