Additional Information; Scsi Protocol; Priority Of Scsi Status Byte Reporting; Invalid Lun In Identify Message - Hitachi HUS151473VL3800 - Ultrastar 73.4 GB Hard Drive Specifications

20.0 Additional information

This chapter provides additional information or descriptions of various functions, features, or operating models supported by
the Target that are not fully described in previous chapters.

20.1 SCSI Protocol

There are various operating conditions that prevent the Target from executing a SCSI command. This section describes each of
these operating conditions and their relative priority.

20.1.1 Priority of SCSI Status Byte Reporting

After establishing the I_T_L nexus or I_T_L_Q nexus the Target must first determine whether command execution is allowed.
Execution is deferred until a later time if the command must be added to the command queue. Execution may also be pre-
vented by an internal Target condition that requires the reporting of a Check Condition, Queue Full, Busy, or Reservation Con-
flict Status. There are several different internal conditions to be active at the same time. The order in which the Target checks
for each of these conditions determines their priority (highest priority first) as follows:
1. Check Condition status for invalid Logical Unit Number. (See Section 20.1.2, "Invalid LUN in Identify Message" on
page 259)
2. Check Condition status for Incorrect Initiator Connection (See Section20.1.3, "Incorrect Initiator Connection" on
page 228)
3. Check Condition status for Unit Attention Condition (See Section 20.1.5, "Unit Attention Condition" on page 230
4. Busy Status or Queue Full Status (See 20.1.4, "Command Processing During Execution of Active I/O Process" on
page 228
5. Check Condition status for Deferred Error Condition (See Section 20.1.8, "Deferred Error Condition" on page 231)
6. Check Condition status during Startup and Format operations (See Section "20.1.6, "Command processing during star-
tup and format operations" on page 231)
7. Reservation Conflict status (See Section 20.1.10, "Command Processing while Reserved" on page 239)
8. Check Condition status for invalid command opcode
9. Check Condition status for invalid command descriptor block
The highest priority internal condition that prevents command execution is reported by the Target provided there is no bus
error.
For all Check Conditions Sense data is built by the target provided a valid LUN address is known. Sense data is cleared by the
Target upon receipt of any subsequent command to the LUN from the initiator receiving the Check Condition.

20.1.2 Invalid LUN in Identify Message

There are three different circumstances defined within the SCSI protocol when the response to an invalid LUN will occur.
Each of these result in a different response.
20.1.2.1 Case 1 - Selection message sequence with Inquiry command
The INQUIRY command is a special case in SCSI. It is used to configure the bus when the drive ID's and LUN's are not
known. The proper response is to return the inquiry data with a peripheral drive type of 1Fh which indicates that the specified
LUN is not supported.
20.1.2.2 Case 2 - Selection message sequence with any other command
Any other commands except REQUEST SENSE return CHECK CONDITION status when an invalid LUN is specified in the
message sequence following selection. In response to a REQUEST SENSE command the target shall return sense data. The
sense key shall be set to ILLEGAL REQUEST and the additional sense code shall be set to LOGICAL UNIT NOT SUP-
PORTED.
Hitachi Ultrastar 15K147 SCSI Hard Disk Drive Specification
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