Quantum Scalar 218FC User Manual page 86

Bit 7
Byte
n
0
N+1
Your ADIC Scalar 218FC supports the Peripheral Device Addressing Method and the Logical Unit
Addressing Method, depending on the configuration of the Fibre Channel device. Discussion of the behavior
of the Fibre Channel device in the different addressing modes follows.
SCC Addressing Option
When an FCR device is configured to use SCC addressing, the unit is capable of responding as a controller
device to the FCP Initiator, or routing the FCP request to a specified BUS:TARGET:LUN. When a request
using the Peripheral Device Addressing Method is received (An FCP command with the LUN field with bits
7 and 6 of byte 0 are set to 0), the unit routes the request to the internal processor, which acts on the
command directly. When a request using the Logical Unit Addressing Method is received (bits 7 and 6 set to
10b), the request is routed to the BUS:TARGET:LUN as specified in the defined field.
Host systems using SCC addressing typically use the Peripheral Device Addressing method to perform initial
device discovery. On issuing an INQUIRY command, the host receives the FCR Inquiry data, indicating that
the device type is a controller device. (Inquiry data indicates device type is 0xC.) On the basis of this data,
the host then knows that subsequent commands to attached devices are to use the Logical Unit Addressing
method. The host can perform discovery by either walking through the BUS:TARGET:LUN values as
would a standard SCSI driver, or by issuing a REPORT LUNS command. This command is sent to the
controller (using the Peripheral Device Addressing Method), and returns a table indicating attached devices.
The host can then perform actions on these devices directly without having to perform discovery through all
possible combinations.
Indexed Addressing Option
Indexed Addressing allows host bus adapter drivers that only use Peripheral Device Addressing to access
SCSI devices attached to the FCR unit. This is done by use of a table that is indexed by sequential LUN
values, indicating selected BUS:TARGET:LUN devices. It is not possible in this mode to address the FCR
unit as a controller unit directly. The table has the structure as shown in Table 5. The maximum size of the
table is equal to the number of busses times the number of targets per bus, less one initiator ID per bus, times
the number of LUNs per target. The index table can be manually edited. Configuration tools allow for the
table to be filled in order of increasing bus, target, or LUN, as may be desired for the specific requirements.
A method is also provided to perform device discovery, and fill the table in the order that devices are
discovered on the SCSI busses.
76 FC to SCSI Mapping
6 5 4
0
Target/LUN
Peripheral Device Addressing
3 2 1
Bus
0