Quantum DLT 2500, Product Manual

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DLT2000 SCSI Interface
DLT2000/DLT2700 Cartridge Tape Subsystem 8-101
8.4.18 REQUEST SENSE (03h)
Bit
7 6 5 4 3 2 1 0
0 Operation Code (03h)
Logical Unit Number Reserved
Reserved
Byte
Allocation Length
Unused Flag Link
1
Reserved
2
Reserved
3
4
5
Figure 8-69 REQUEST SENSE CDB
REQUEST SENSE tells the target to transfer 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
target until retrieved by the REQUEST SENSE command, or until the receipt of any
other command from the same initiator.
If the drive receives an unsolicited REQUEST SENSE, then it returns Sense Data with
the appropriate values in the EOM, Sense Key, Additional Sense Code, and Additional
Sense Code Qualifier. The positional information provided reflects the logical position
of the drive. The drive returns information based on the (nondiagnostic) data still in its
buffer as well as the data on tape.
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 media, it should
precede the REQUEST SENSE with a WRITE FILEMARKS with length 0 (Immed =0)
command, which forces the drive to flush any currently buffered data to tape. A
subsequent REQUEST SENSE will return the actual physical (and logical) position of
the drive to the initiator.
Allocation Length
The Allocation Length specifies the maximum number of sense bytes to be returned.
The drive terminates the transfer when Allocation Length bytes have been transferred or
when all available sense data has been transferred to the host, whichever is less.