Sony DDS-4 Product Description Manual page 92

6. COMMAND SPECIFICATION
RED:
The report exception on decompression (RED) field indicates the device's response to a boundary condition caused
by a change in the format of recorded data from:
uncompressed to compressed
or
compressed to uncompressed
This field only has an effect during reading not during writing.
RED=00b When the RED field = 00b, the drive will report a CHECK CONDITION status (MEDIUM ERROR)
whenever data is encountered on the media that the drive cannot decompress.
The SDT-10000/SDT-11000 will not report CHECK CONDITION at a boundary condition as long as the data is
uncompressed or DCLZ compressed.
RED=01b A RED field of 01b is undefined and the drive will issue a CHECK CONDITION status with the sense
key set to ILLEGAL REQUEST.
RED=10b When the RED field = 10b, the drive shall return a CHECK CONDITION status whenever a boundary
condition is encountered on the medium. The boundary conditions are:
from uncompressed to compressed
or
from compressed to uncompressed
CHECK CONDITION will be reported on the boundary condition even if the drive supports hardware decompres-
sion.
For any of the boundary conditions which result in a CHECK CONDITION status, the additional sense code shall
be set to either DECOMPRESSION EXCEPTION, ALGORITHM ID OF NN. The drive will set the decompres-
sion algorithm field to the algorithm identifier of the compression algorithm used to process the encountered data.
The device shall be positioned on the EOP side of the encountered data, and the command-specific information field
in the sense data shall contain a count of the number of data blocks contained within the encountered data.
Note: When compressed data is encountered on the medium which the device cannot decompress, the device should
treat the data as a single variable-length record. In the sense data, the valid bit, the ILI bit and the information
field should be set accordingly.
RED=11b A RED field of 11b is undefined and the drive will issue a CHECK CONDITION status with the sense
key set to ILLEGAL REQUEST.
Compression Algorithm:
The compression algorithm field indicates the compression algorithm the drive will use to process data sent to it by
the initiator (if the DCE bit is one).
The SDT-10000/SDT-11000 supports the DCLZ data compression algorithm which is identified by the value: 00 00
00 20h in the compression algorithm field. A value of zero shall indicate that no compression algorithm is currently
selected. Any other values in this field will cause the drive to return a CHECK CONDITION status the sense key
shall be set to ILLEGAL REQUEST.
Decompression Algorithm:
For MODE SELECT the decompression algorithm field indicates the decompression algorithm selected by the
initiator for use in subsequent decompression of data encountered on the medium.
The SDT-10000/SDT-11000 can decompress data recorded with the DCLZ algorithm therefore this field can be set
to 00 00 00 20h. However, the SDT-10000/SDT-11000 is capable of automatic recognition of the compression
algorithm used to process the data encountered on the medium. Therefore, the drive will override the value in the
decompression field (if is set to zero) for a subsequent read operation when DCLZ compressed data is detected on
the media.
SONY SDT-10000/SDT-11000 DDS Tape Drive
MODE SELECT
6 - 41