M2488 PRODUCT GUIDE
TAPE UNIT SCSI COMMANDS
April 1997
CG00000-011503 REV. A
4-101
4-3.22
RELEASE UNIT command 17h
The RESERVE UNIT and RELEASE UNIT commands serve to resolve contention in multiple-initi-
ator systems. The RELEASE UNIT command is used to release previously reserved logical units for
the requesting initiator, or if it is a third-party release, for another specified SCSI device.
The SCSI device that releases the reservation of the tape logical unit, also automatically releases the
reservation of the medium changer logical unit, even though the RELEASE UNIT command was
directed to the tape logical unit. This is because the SCSI device that gains the reservation of the tape
logical unit also automatically gains the reservation of the medium changer logical unit.
The RESERVE UNIT and RELEASE UNIT commands are not supported for the medium changer
logical unit, however, releasing the reservation of the tape logical unit will serve as a method of
releasing the medium changer logical unit as well.
4-3.22.1
RELEASE UNIT CDB Description
RELEASE UNIT is a six-byte command. The bytes are shown below and described in Table 4-98.
Common fields are described in paragraph 4-3.1 on page 4-4
.
BITS
BYTES
7
6
5
4
3
2
1
0
0
0
0
0
1
0
1
1
1
1
LUN
3rd Party
3rd Party Dev ID
Reserved
2
Reserved
3
Reserved
4
Reserved
5
Reserved
Flag
Link
Note: Changeable fields in the CDB are shaded.
Table 4-98. RELEASE UNIT Field Description
BYTE
BIT
VALUE
DESCRIPTION
0
0-7
17h
Operation Code.
1
1-3
The 3rd Party Dev ID is the SCSI device for whom a third-party reserva-
tion has been made.
1
4
0
If the 3rd Party bit is zero, then the initiator that made the non-third-party
reservation, releases the reserved device.
1
If the 3rd Party bit is one, the initiator that made a third-party reservation
for the device specified in the “3rd Party Dev ID” field releases the reser-
vation for that same device.
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