SCSI Primary Commands - 2.pdf

18 July 2001 T10/1236-D Revision 207.20 REQUEST SENSE command7.20.1 REQUEST SENSE command introductionThe REQUEST SENSE command (see table 101) requests that the device server transfer sense data to the applicationclient.Table 101 — REQUEST SENSE commandBitByte7 6 5 4 3 2 1 00 OPERATION CODE (03h)1 Reserved2 Reserved3 Reserved4 ALLOCATION LENGTH5 CONTROLSense data shall be available and cleared under the conditions defined in SAM-2. If the device server has no othersense data available to return, it shall return a sense key of NO SENSE and an additional sense code of NOADDITIONAL SENSE INFORMATION.If the device server is in the standby power condition or idle power condition when a REQUEST SENSE commandis received and there is no ACA or CA condition, the device server shall return a sense key of NO SENSE and anadditional sense code of LOW POWER CONDITION ON. On completion of the command the logical unit shallreturn to the same power condition that was active before the REQUEST SENSE command was received. AREQUEST SENSE command shall not reset any active power condition timers.The device server shall return CHECK CONDITION status for a REQUEST SENSE command only to reportexception conditions specific to the command itself. For example:a) An invalid field value is detected in the CDB;b) An unrecovered parity error is detected by the service delivery subsystem; orc) A target malfunction that prevents return of the sense data.If a recovered error occurs during the processing of the REQUEST SENSE command, the device server shallreturn the sense data with GOOD status. If a device server returns CHECK CONDITION status for a REQUESTSENSE command, the sense data may be invalid.NOTE 28 The sense data appropriate to the selection of an invalid logical unit is defined in SAM-2.Device servers shall be capable of returning eighteen bytes of data in response to a REQUEST SENSE command.If the allocation length is eighteen or greater, and a device server returns less than eighteen bytes of data, theapplication client should assume that the bytes not transferred would have been zeros had the device serverreturned those bytes. Application clients may determine how much sense data has been returned by examiningthe ALLOCATION LENGTH field in the CDB and the ADDITIONAL SENSE LENGTH field in the sense data. Device serversshall not adjust the additional sense length to reflect truncation if the allocation length is less than the sense dataavailable.dpANS SCSI Primary Commands - 2 (SPC-2) 135