Read Position Command (34H) - Quantum DLT 8000 Product Manual

5.17 READ POSITION Command (34h
The READ POSITION command is used to read a position identifier or SCSI Logical
Block Address (LBA). The LOCATE command uses this identifier to position back to
this same logical position in a high-performance fashion.
Bit 7
Byte
0
1
2 - 8
9 Unused
Figure 5–77 READ POSITION Command Descriptor Block — Data Format
Table 5–76 READ POSITION Command Descriptor Block — Field Descriptions
Field Name
TCLP
Long
BT
6 5
Logical Unit Number
Description
Total Current Logical Position. When = 1, data returned includes
block, filemark, and setmark position and fits format described in
Section 5.17.2. When = 0, the data takes the SCSI-2 format described
in Section 5.17.1.
This bit indicates the drive returns data specifying the partition, file,
and set number with the current logical position (long form). A TCLP
bit of 0 indicates the device server will return data specifying the first
and last block location with the number of bytes and blocks in the
buffer (short form).
When the Long bit = 1, it indicates the server will return 32 bytes of
data; a value of 0 indicates the device server will return 20 bytes of
data. Both the Long bit and the TCLP bit must both be set to 1 or 0. If
these bits have different values, the drive returns CHECK CONDITION,
ILLEGAL REQUEST.
Block Type. This bit indicates how the position is to be interpreted.
Since the tape drive uses the same logical block regardless of the
setting of this bit, the setting is ignored. The logical block address
values include all recorded objects: blocks and filemarks.
Quantum DLT 8000 Tape System
)
4 3
Operation Code (34h)
Rsv'd
Reserved
Reserved
SCSI Commands
2 1
TCLP Long
Flag
0
BT
Link
5-169