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SCSI Commands
Quantum DLT 7000 Tape System 5-145
REQUEST SENSE Command (03h) (continued)
The REQUEST SENSE command causes the tape drive to transfer detailed sense
data to the initiator.
The sense data is valid for a CHECK CONDITION or RESERVATION
CONFLICT status returned on the previous command. The sense data bytes are
preserved by the tape drive until retrieved by a REQUEST SENSE command, or
until the receipt of any other command from the same initiator, though some
commands, such as INQUIRY, do not change sense data.
If the tape drive receives an unsolicited REQUEST SENSE, it returns sense data
with the appropriate values in the End of Media (EOM), Sense Key, Additional
Sense Code, and Additional Sense Code Qualifier. The positional information
provided reflects the logical position of the tape drive. The tape drive returns
information based on the non-diagnostic data in its buffer as well as the data on
tape medium. Additionally, bytes 25 through 28 contain the amount of tape to
be written in 4 KB blocks.
REQUEST SENSE does not cause the drive to flush its buffered data to tape.
Therefore, if the host requires the exact physical positioning of the tape medium,
it should precede the REQUEST SENSE command with a WRITE FILEMARKS
command with length 0 (Immed=0) specified. This forces the tape drive to flush
any currently-buffered data to tape. A subsequent REQUEST SENSE command
returns the actual physical (and logical) position of the tape drive to the
initiator.
The following illustration portrays the format of REQUEST SENSE DATA.