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TAPE UNIT SCSI COMMANDS
4-3.25
RESERVE UNIT command 16h
The RESERVE UNIT and RELEASE UNIT commands serve to resolve contention in multiple-initi-
ator systems. The RESERVE UNIT command reserves the specified logical unit for the exclusive use
of the requesting initiator, or if it is a third-party reservation, for another specified SCSI device.
The SCSI device that gains the reservation of the tape logical unit, also automatically gains the reser-
vation of the medium changer logical unit, even though the RESERVE UNIT command was directed
to the tape logical unit.
The RESERVE UNIT command is not supported for the medium changer logical unit, however, res-
ervation of the tape logical unit will serve as a method of reserving the medium changer logical unit
as well. The reservation on the medium changer logical unit will be released when a RELEASE
UNIT command is issued for the tape logical unit.
4-3.25.1
RESERVE UNIT CDB Description
RESERVE UNIT is a six-byte command. The bytes are shown below and described in Table 4-
105. Common fields are described in paragraph 4-3.1 on page 4-4
BYTES
7
0
0
1
2
3
4
5
Note: Changeable fields in the CDB are shaded.
BYTE
BIT
VALUE
0
0-7
1
1-3
1
4
4-112
6
5
4
0
0
1
LUN
3rd Party
Reserved
Table 4-105. RESERVE UNIT Field Description
16h
Operation Code.
The 3rd Party Device ID specifies the SCSI device the reservation is for.
This field is ignored when bit 4=0.
Third Party Reservation allows an initiator to reserve a logical unit for
another SCSI device.
If the 3rd Party bit is zero, then the RESERVE UNIT command is to
reserve the logical unit for the initiator sending the command.
If the 3rd Party bit is one then the logical unit will be reserved for the SCSI
device specified in the 3rd Party Dev ID field.
CG00000-011503 REV. A
M2488 PRODUCT GUIDE
.
BITS
3
2
0
1
3rd Party Dev ID
Reserved
Reserved
Reserved
DESCRIPTION
1
0
1
0
Reserved
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April 1997
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