Quantum DLT1/VS80 SCSI, Interface Manual

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DLT1/VS80 SCSI Interface Guide
81-81276-01 Rev A01 July 2004 4-15
4.6 LOCATE (2Bh)
Use the LOCATE command for high-speed positioning to the specified block address.
Figure 4-10. LOCATE (2Bh) Command Descriptor Block — Data Format
When writing, use the READ POSITION command to obtain the block address where particular
blocks of data (for example, a data file) are about to be written. Then use the LOCATE command to
position back to the same logical position for high performance restore operations of particular blocks
of data.
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation Code (2Bh)
1 Logical Unit Number Reserved BT CP Immed
2 Reserved
3 - 6
(MSB)
Block Address
(LSB)
7 Reserved
8 Partition
9 Unused Reserved Flag Link
Table 4-8. LOCATE (2Bh) Command Descriptor Block — Field Descriptions
Field Name Description
LUN Logical Unit Number. The target ignores this field. Only an IDENTIFY message
can change the LUN.
BT Block Type. This bit indicates how the Block Address field is interpreted. The tape
drive always returns SCSI Logical Block addresses; that is, setting the BT bit does
not affect the values returned. The first recorded object (block or filemark) is at
address 0, and Block Addresses count both data blocks and filemarks.
CP Change Partition. Since the drive does not support multiple partitions, this bit must
be 0.
Immed Immediate. When 1, the drive returns status as soon as the operation starts. When
0, the drive returns status after the operation has completed.