SCSI Commands: 40BREQUEST SENSE Page 1683.28 REQUEST SENSEThe REQUEST SENSE command returns the status of the last command.Sense Data is updated with each command; therefore, the sense data only reportsthe status of the immediately previous command. If a Check Condition statusresults, a REQUEST SENSE command should be issued to recover the informationform the Sense Data.The REQUEST SENSE command returns Check Condition status only if a fatal erroroccurs during execution of the REQUEST SENSE command. If nonfatal errors occurduring the REQUEST SENSE execution, Good Status is returned. Sense Data maybe invalid following a fatal error on a REQUEST SENSE command.3.28.1 Sense Data ManagementThe drive maintains three types of sense data.♦ Current Sense is sense data associated with the last command received fromthe 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 commandwith the immediate bit set or may be a buffered write. A command with theimmediate bit of one will generate sense for the host that sent the command. Abuffered write will generate sense for all hosts.♦ Unit Attention Sense is sense data generated by a Unit Attention condition. Thisis generated for all hosts.Any command other than a REQUEST SENSE command or an INQUIRY commandwill generate Check Condition status if there is Deferred Sense data or UnitAttention data available. All commands will generate Check Condition status if thecommand itself generates sense data. If the next command after the CheckCondition status is not a REQUEST SENSE command, then all the sense data forthat initiator is cleared.When a REQUEST SENSE command is received, the Current Sense is returned. Ifthere is no Current Sense, the Deferred Sense is returned. If there is no DeferredSense, 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 beenreturned, that sense data is cleared. Any other sense data that is still pending maystill cause Check Condition status for subsequent commands.
