140 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
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5.2.1.8
Reserve Command (16h)
The Reserve and Release commands provide the basic mechanism for contention resolution in multiple
initiator systems. The third party reservation allows one initiator to reserve the drive for some other SCSI
device that can act as an initiator. Table 5.2.1-16 shows the command structure.
Table 5.2.1-16. Reserve Command CDB
Bit
7
6
5
4
3
2
1
0
Byte(s)
0
0
0
0
1
0
1
1
0
1
Logical Unit No.
[1] 3rd
3rd PRTY DEV.ID EXTENT
PRTY
0
0
0 0 or 1 [2]
[2]
[3]
2
RESERVATION IDENTIFICATIONS
0
0
0
0
0
0
0
0 [4]
3
EXTENT LIST LENGTH (MSB)
0
0
0
0
0
0
0
0 [3]
4
EXTENT LIST LENGTH (LSB)
0
0
0
0
0
0
0
0 [3]
5
0
0
0
0
0
0 Flag Link [5]
Notes.
[1] The LUN must be zero.
[2] If bit 4 is zero, bits 3, 2, and 1 are zeros. If bit 4 is one, bits 3, 2, and 1 identify the SCSI bus ID of the
device for which the drive is reserved.
[3] Must be zero if not supported. Check with drive Product Manual, “SCSI Interface commands supported”.
.
[4] Reserve Identifications applies only if Extent is supported. This field must be zero if not supported. Check
with drive Product Manual, section “SCSI Interface commands supported”. (also see paragraph 5.2.1.8.1,
5.2.1.8.2).
[5] See “Control Byte” paragraph 4.2.6.
5.2.1.8.1
Logical Unit Reservation
If the Extent bit is zero, this command requests the entire disc drive be reserved for exclusive use of the
initiator until the reservation is superseded by another valid Reserve command from the initiator that made
the reservation, released by a Release command from the same initiator, by a Bus Device Reset message
from any initiator, or by a “hard” Reset condition. A logical unit reservation is not granted if any extent or
logical unit is reserved by another initiator or if any extent with a read shared reservation type is reserved by
this initiator. It is permissible for an initiator to reserve a logical unit that is currently reserved by that initiator.
If the Extent bit is zero, the Reservation Identification and the Extent List Length are ignored. If the Extent bit
is a one and if the drive does not support the extent reservation option, the disc drive generates Check
Condition status and sets the sense key to Illegal Request.
If, after honoring the reservation, any other initiator subsequently attempts to perform a command other than
a Release command, which shall be ignored, or an Inquiry command, which shall be executed, or a Request
Sense command, which shall be executed, the command is rejected with Reservation Conflict status.
