Maxtor ATLAS 10K III Product Manual page 198

SCSI Description
      5 V C V W U 4 G R Q T V K P I
The drive returns CHECK CONDITION status for a REQUEST SENSE command
only to report errors specific to the command when:
• A non-zero reserved bit is detected in the Command Descriptor Block.
• A drive malfunction prevents return of the sense data.
For Parallel SCSI disk drives, the drive also returns CHECK CONDITION status for
a REQUEST SENSE command to report errors specific to the command when an
unrecovered parity error is detected on the data bus.
Note that any of the previous conditions overwrites the current sense data with the
sense data describing the error encountered by the REQUEST SENSE command
(that is, for the condition stated in the first bulleted entry, the new sense data reflects
that a non-zero reserved bit was detected in the Command Descriptor Block).
The drive returns a maximum of 18 bytes of sense data. The initiator should set the
Allocation Length field in the Command Descriptor Block to 18 to receive all sense
data. If the Allocation Length is set to 0, four bytes of data will be returned (this option
maintains compatibility with SCSI-1 systems).
5-134 Maxtor Atlas 10K III