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6.Command Specification
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.
8 = size of the Block Access Table (BAT) of the AIT Group.
AIT2:
1202,688 = size of AIT Group.
40 = size of the Group Information Table (GIT) of the AIT Group.
8 = size of the Block Access Table (BAT) of the AIT Group.
AITE Turbo:
1202,688 = size of AIT Group.
40 = size of the Group Information Table (GIT) of the AIT Group.
8 = size of the Block Access Table (BAT) of the AIT Group.
AIT1 Turbo:
1202,688 = size of AIT Group.
40 = size of the Group Information Table (GIT) of the AIT Group.
8 = size of the Block Access Table (BAT) of the AIT Group.
AIT2 Turbo:
2405,376 = size of AIT Group.
40 = size of the Group Information Table (GIT) of the AIT Group.
4 = size of the Block Access Table (BAT) 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.
6-38
SONY AIT-2 Turbo drive SDX-550V series Ver.1.0
MODE SELECT
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