SCSI Primary Commands - 2.pdf

18 July 2001 T10/1236-D Revision 20An incorrect length indicator (ILI) bit of one usually indicates that the requested logical block length did not matchthe logical block length of the data on the medium. Examples of other conditions indicated by the ILI bit being set toone include media interchange incompatibilities where the recorded logical block length is too large for the deviceserver to read.The SENSE KEY, ADDITIONAL SENSE CODE and ADDITIONAL SENSE CODE QUALIFIER fields provide a hierarchy of information.The intention of the hierarchy is to provide a top-down approach for an application client to determine informationrelating to the error and exception conditions. The sense key provides generic categories in which errorand exception conditions may be reported. Application clients typically use sense keys for high level error recoveryprocedures. Additional sense codes provide further detail describing the sense key. Additional sense code qualifiersadd further detail to the additional sense code. The additional sense code and additional sense code qualifiermay be used by application clients where sophisticated error recovery procedures require detailed informationdescribing the error and exception conditions.The SENSE KEY field is mandatory and indicates generic information describing an error or exception condition. Thesense keys are defined in 7.20.6.The contents of the INFORMATION field is device-type or command specific and is defined within the appropriatestandard for the device type or command of interest. Device servers shall implement the INFORMATION field.Unless specified otherwise, this field contains:a) the unsigned logical block address associated with the sense key, for direct-access devices (device type 0),write-once devices (device type 4), CD-ROM devices (device type 5), and optical memory devices (devicetype 7). If the logical block address value cannot be represented in four bytes, the VALID bit shall be set tozero;b) the difference (residue) of the requested length minus the actual length in either bytes or blocks, as determinedby the command, for sequential-access devices (device type 1), printer devices (device type 2),processor devices (device type 3) and some direct access device commands, except as defined for d)below. Negative values are indicated by two's complement notation;c) the difference (residue) of the requested number of blocks minus the actual number of blocks copied orcompared for the current segment descriptor of an EXTENDED COPY command; ord) for sequential-access devices operating in buffered modes 1h or 2h that detect an unrecoverable writeerror when unwritten data blocks, filemarks, or setmarks remain in the buffer, the value of the INFORMATIONfield for all commands shall be:A) the total number of data blocks, filemarks, and setmarks in the buffer if the device is in fixed blockmode (i.e., BLOCK LENGTH field of the MODE SENSE block descriptor is non-zero and the FIXED bit ofthe WRITE command is one); orB) the number of bytes in the buffer, including filemarks and setmarks, if the device is in variable mode(i.e., the FIXED bit of the WRITE command is zero).For additional information on the use of the INFORMATION field by sequential-access devices see SSC.The ADDITIONAL SENSE LENGTH field indicates the number of additional sense bytes to follow. If the allocation lengthof the CDB is too small to transfer all of the additional sense bytes, the additional sense length is not adjusted toreflect the truncation.The COMMAND-SPECIFIC INFORMATION field contains information that depends on the command that encountered theexception condition. Further meaning for this field is defined within the command description. TheCOMMAND-SPECIFIC INFORMATION field is mandatory if the device server supports any of the following commands:EXTENDED COPY and REASSIGN BLOCKS.The additional sense code (ASC) indicates further information related to the error or exception condition reportedin the SENSE KEY field. Device servers shall support the ADDITIONAL SENSE CODE field. Support of the additionalsense codes not explicitly required by this standard is optional. A list of additional sense codes is in 7.20.6. If thedpANS SCSI Primary Commands - 2 (SPC-2) 137