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SCSI Commands Reference Manual, Rev. J 37
www.seagate.com General Concepts
2. General Concepts
This manual defines behaviors that are common to all Seagate SCSI device models. This manual defines the SCSI commands that
are basic to more than one disk drive model and the SCSI commands that may apply to any SCSI Interface, including Fibre
Channel and Serial Attached SCSI (SAS).
2.1 Command Descriptor Block (CDB)
2.1.1 CDB usage and structure
A command is communicated by sending a command descriptor block (CDB) to the device server. For several commands, the
CDB is accompanied by a list of parameters in the Data-Out Buffer. See the specific commands for detailed information.
If a logical unit validates reserved CDB fields and receives a reserved field within the CDB that is not zero, then the logical unit
shall terminate the command with CHECK CONDITION status, with the sense key set to ILLEGAL REQUEST, and the additional
sense code set to INVALID FIELD IN CDB.
If a logical unit receives a reserved CDB code value in a field other than the OPERATION CODE field, then the logical unit shall
terminate the command with CHECK CONDITION status, with the sense key set to ILLEGAL REQUEST, and the additional sense
code set to INVALID FIELD IN CDB.
The fixed length CDB formats are described in 2.1.2. The variable length CDB formats are described in 2.1.4. The CDB fields that
are common to most commands are described in 2.1.5. The fields shown in 2.1.2 and 2.1.3 and described in 2.1.4 are used
consistently by most commands. However, the actual usage of any field (except OPERATION CODE and CONTROL) is described in
the subclause defining that command. If a device server receives a CDB containing an operation code that is invalid or not
supported, the command shall be terminated with CHECK CONDITION status, with the sense key set to ILLEGAL REQUEST, and
the additional sense code set to INVALID COMMAND OPERATION CODE.
For all commands, if there is an invalid parameter in the CDB, the device server shall terminate the command without altering
the medium.