Quantum DLT 2500, Product Manual

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DLT2000 SCSI Interface
DLT2000/DLT2700 Cartridge Tape Subsystem 8-27
8.4.6 LOCATE (2Bh)
Bit
7 6 5 4 3 2 1 0
0 Operation Code (2Bh)
Logical Unit Number BT CP Imm
Byte
(MSB)
Block Address
(LSB)
Unused Flag Link
Reserved 1
Reserved 2
Reserved
3
Partition
4
Reserved
5
6
7
8
9
Figure 8-11 LOCATE CDB
The LOCATE command is used to do high-speed positioning to the specified block
address. Average positioning time is about 45 seconds; maximum time is under 90
seconds.
The READ POSITION command can be used to obtain the block address, when
Writing, where particular blocks of data (for example, a data file) are about to be
written. Then the LOCATE command can be used to position back to the same logical
position for high performance restore operations of particular blocks of data.
•
BT - The Block Type bit indicates how the Block Address field is interpreted. For
the DLT2000 products, SCSI Logical Block addresses are always returned, that is,
setting the BT bit does not affect the values returned. The first recorded object
(block or filemark) is at address zero, and Block Addresses count both data blocks
and filemarks.
•
CP - Since multiple partitions are not supported this bit must be zero.
•
Imm - If set, STATUS is returned when the command has been started.
Block Address
The Block Address field defines the SCSI Logical Block Address to which the media
will be positioned. These addresses start at zero, and include data blocks and filemarks,
so they could also be considered an object address.