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CHAPTER 4
SENSE DATA ERROR RECOVERY METHODS
4.1
Sense Data
4.2
INIT Error Recovery Methods (Recommended)
4.3
Disk Drive Error Recovery Methods
In this chapter, the configuration and contents of sense data reported to the INIT (initiator) when an
error occurs, etc., key information for interpreting error states, recommended procedures for error
recovery processing that should be executed by software in the INIT and error recovery processing
executed internally by the IDD are described. Furthermore, see Chapter 3, “SCSI Bus Error Recovery
Processing” in the “SCSI Physical Interface Specifications” concerning recovery processing for errors
detected in operations on the SCSI bus.
4.1
Sense Data
When the IDD reports a CHECK CONDITION status, or in cases when some fatal error is
detected in connection with the SCSI bus, and as a result, the command that is currently being
executed, or the commands in the stack are cleared, it generates sense data for the INIT that
issued that command. The INIT can fetch the sense data by issuing a REQUEST SENSE
command.
4.1.1
Sense Data Format
The IDD’s sense data is in the so-called “Expanded Sense Data” format. The expanded sense
data format supported by the IDD is shown in Fig. 4.1.
Notes:
1.
In the SCSI specifications, each device is permitted to define whatever it chooses after
byte 18 of the expanded sense data, and the length and format differ for each device.
The length of expanded sense data is displayed in the sense data, so by analyzing the
sense data which it receives, the INIT can know its effective length.
2.
In the REQUEST SENSE command, even if a “Transfer byte” length that is shorter
than the length of the sense data supported by the device which is the object of the
command, the command will terminate normally, but in that case, some of the sense
data only will be received and the remaining information will be lost. Sufficient
caution should be exercised with regard to the devices connected to the INIT and all
the sense data of those devices should be read.
