- ATTO FibreBridge Installation & Operations Manual

ATTO Technology, Inc. ATTO FibreBridge Installation & Operation Manual
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ATTO Technology, Inc.
SCSI Target Identifier
The SCSI Target Identifier indicates the SCSI ID assigned to the target. Each device on the same
physical SCSI bus must be assigned a unique SCSI ID. A Wide (16-bit) SCSI bus will support a maximum
of 16 SCSI IDs (including the SCSI ID assigned to the FibreBridge).
SCSI Logical Unit Number
The SCSI Logical Unit Number indicates the logical unit being addressed within the specified target.
SCSI Architecture Model (SAM-2) Logical Unit Addressing
The SCSI Architecture Model – 2 (SAM-2) specification defines a reference model that specifies common
behaviors for SCSI devices, and an abstract structure that is generic to all SCSI-3 I/O system
implementations. The structure for Logical Unit Addressing is detailed below.
What is a Logical Unit?
A logical unit is the entity that executes SCSI Commands sent by SCSI initiators. A logical unit is
addressed by a Logical Unit Number (LUN). A LUN is represented by a 64-bit number in Fibre Channel
and a 5-bit number in parallel SCSI. The FibreBridge will map between an 8-byte (64-bit) Fibre Channel
LUN and a parallel SCSI LUN.
Hierarchical Addressing Model
SAM-2 defines the concept of hierarchical LUN addressing and the four addressing levels that are
supported. The hierarchical LUN address is shown in the table below.
Bit
Byte
7 6 5 4 3 2 1 0
0 (MSB)
1
First level addressing field
(LSB)
2 (MSB)
3
Second level addressing field
(LSB)
4 (MSB)
5
Third level addressing field
(LSB)
6 (MSB)
7
Fourth level addressing field
(LSB)
The FibreBridge implements a single level of hierarchical LUN addressing by using the 16-bit “First Level
Addressing Field”. The contents of the second, third and fourth level addressing fields are ignored by the
FibreBridge.
Addressing Field Format
Each of the four addressing level fields is structured as a 16-bit value with the following format.