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Page 98
REQUEST SENSE
Sense Data Management
Command Descriptor Block
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.
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 flag set or may be a buffered write. A command with the
Immediate flag set 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.
Bits
Byte
7
6
0
1
Ignored LUN
2
3
4
5
5
4
3
Operation Code (03h)
Reserved
Reserved
Reserved
Allocation Length
Control
LTO SCSI Interface Manual
2
1
0
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