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SCSI Commands: 40BREQUEST SENSE
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3.28
REQUEST SENSE
The REQUEST SENSE command returns the status of the last command.
Sense Data is updated with each command; therefore, the sense data only reports
the status of the immediately previous command. If a Check Condition status
results, a REQUEST SENSE command should be issued to recover the information
form the Sense Data.
The REQUEST SENSE command returns Check Condition status only if a fatal error
occurs during execution of the REQUEST SENSE command. If nonfatal errors occur
during the REQUEST SENSE execution, Good Status is returned. Sense Data may
be invalid following a fatal error on a REQUEST SENSE command.
3.28.1
Sense Data Management
The drive maintains three types of sense data.
♦
Current Sense is sense data associated with the last command received from
the initiator.
♦
Deferred Sense is sense data from a command that has been reported as good,
but has generated sense data after being reported. This may be a command
with the immediate bit set or may be a buffered write. A command with the
immediate bit of one will generate sense for the host that sent the command. A
buffered write will generate sense for all hosts.
♦
Unit Attention Sense is sense data generated by a Unit Attention condition. This
is generated for all hosts.
Any command other than a REQUEST SENSE command or an INQUIRY command
will generate Check Condition status if there is Deferred Sense data or Unit
Attention data available. All commands will generate Check Condition status if the
command itself generates sense data. If the next command after the Check
Condition status is not a REQUEST SENSE command, then all the sense data for
that initiator is cleared.
When a REQUEST SENSE command is received, the Current Sense is returned. If
there is no Current Sense, the Deferred Sense is returned. If there is no Deferred
Sense, the Unit Attention Sense is returned. If there is no Unit Attention Sense,
default sense data is returned. Once a particular set of sense data has been
returned, that sense data is cleared. Any other sense data that is still pending may
still cause Check Condition status for subsequent commands.
Summary of Contents for LTO 4
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