Commands—Introduction 33
Commands—Introduction
■ If no IDENTIFY message is supplied, the LUN is taken from the host’s
Command Descriptor Block.
■ If an IDENTIFY message is supplied, the LUN in the host’s Command
Descriptor Block is ignored
■ If the LUN is unsupported, and the host command is not REQUEST SENSE,
CHECK CONDITION is reported to the host with a sense key of ILLEGAL
REQUEST
, and additional sense of 2500h (logical unit not supported).
■ If the LUN is unsupported, and the host command is REQUEST SENSE, the
original sense data is replaced with a sense key of
ILLEGAL REQUEST, and
additional sense of 2500h (logical unit not supported). This new sense
data is returned to the host. Once the command has completed
successfully, the sense data is cleared.
Deferred Error Check
A deferred error is generated when a command with immediate report fails
after the report has been returned. The check looks to see if a deferred error
exists for the host which sent the command, in other words, a deferred error for
which
CHECK CONDITION status has not yet been reported. If such an error
exists, then the drive reports
CHECK CONDITION. The sense data for the
command is set to
DEFERRED ERROR (which was generated when some
previous command failed).
Note that if a
UNIT ATTENTION condition and a DEFERRED ERROR condition
both exist for an initiator, the
DEFERRED ERROR condition will be reported first.
This is because the operation leading to the deferred error must have been
older than that leading to the unit attention. The drive reports the conditions in
the order in which they arose.
Diagnostic Status Check
This ensures that the drive is in a fit state to access the media. It does this by
checking that there is no
DIAGNOSTIC FAIL status within the drive.
If the drive has failed diagnostics,
CHECK CONDITION is reported with a sense
key of
HARDWARE ERROR and additional sense of 400Xh (diagnostic failure
on component X).
