Sony SDX-700C Product Specifications Manual page 91

MODE SELSECT
If the field is ZERO, then the drive does not report a GOOD status on WRITE commands until the data blocks are
actually written to tape.
If the Buffered Mode field is one, then the drive reports GOOD status on WRITE commands as soon as the data
block has been transferred to the buffer. This is the default configuration for the drive.
If Buffered Mode field is ZERO the drive will operate in non-Buffered Mode. In non-Buffered Mode the drive will not
report SCSI status on a Write Command until all data is on tape, or the write retry is exceeded. The drive may suffer
a significant degradation in capacity and SCSI throughput. If the write data is much smaller than an AIT Group the
unused area of AIT Group will be marked as non data on tape. This AIT Group results in under-utilization of tape
area and therefore a reduction in tape capacity. The next Write Command will create a new AIT Group for Write data
and append to last AIT Group. It will not append to the last record within the unused area of the previous AIT Group.
For example, if the Write Command block size or record size is 4,096 bytes and it is variable block mode and there is
no data in buffer (from a previous buffered Write) the AIT Group will contain only 4,096 bytes of data and (801,792 -
4,096 - (40+8)) = 797,648 bytes of non data on tape. The description of the values for the unused part of the AIT
Group is:
AIT1: 801,792 = size of AIT Group.
40 = size of the Group Information Table (GIT) of the AIT Group.
AIT2: 1202,688 = size of AIT Group.
40 = size of the Group Information Table (GIT) of the AIT Group.
AIT3: 2405,376 = size of AIT Group.
40 = size of the Group Information Table (GIT) of the AIT Group.
The SCSI throughput is reduced because the Write Command is not completed until either all the data is on tape, or
the write retry is exceeded.
Speed: The drive only supports one speed, the default speed. Because of this, this field must be set to ZERO. Any
other value will cause a CHECK CONDITION status with an ILLEGAL REQUEST sense key is returned.
Block Descriptor Length: This specifies the length in bytes of all the block descriptors. Since the drive only allows
one block descriptor, this value must be eight. Any other value will cause a CHECK CONDITION status with an
ILLEGAL REQUEST sense key to be returned.
Note: The block descriptor specifies the media characteristics for the SDX drive. The block descriptor contains the
density code, number of blocks and block length fields.
Density Code: The supported values for the density code field are defined in the following table.
Note: 00h - Default: The use of the word "Default" is SCSI specific. It instructs the drive to use its default or only
density.
Code Value
00h
30h
31h
32h
7Fh
Number of Blocks: A MODE SENSE field which will be returned as ZERO, indicating that all of the remaining logical
blocks on the media will have the medium characteristics specified by the block descriptor, or until a subsequent
MODE SELECT command changes those parameters. This field must be set to ZERO on a MODE SELECT
otherwise a CHECK CONDITION status will be returned with an ILLEGAL REQUEST sense key.
Block length: The Block Length field specifies the length in bytes of each logical block transferred over the SCSI
bus. A block length of ZERO indicates that the length is variable. Any other value indicates the number of bytes per
block that the drive must handshake over the bus. This establishes block length such that the transfer length for
read, write and verify type commands will be a block count not a byte count.
SONY AIT-3 drive SDX-700 series Ver.2.1
4 = size of the Block Access Table (BAT) of the AIT Group.
4 = size of the Block Access Table (BAT) of the AIT Group.
4 = size of the Block Access Table (BAT) of the AIT Group.
Table 6-32: Sequential-Access Density Codes
Code Value
Default Format
AIT-1 Format
AIT-2 Format
AIT-3 Format
No change from previous density
6.Command Specification
6-41