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5.35
Reserve (6) command (16h)
The Reserve and Release commands provide the basic mechanism for contention resolution in multiple initia-
tor systems. The third party reservation allows one initiator to reserve the drive for some other SCSI device that
can act as an initiator. Table 158 shows the command structure.
Table 158:
Reserve (6) command (16h)
Bit
7
Byte
0
0
1
0
Logical Unit Number [1]
2
0
3
0
4
0
5
0
Notes.
[1]
The Logical Unit Number 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 individual drive's Product Manual, Volume 1, section "SCSI
Interface commands supported."
[4]
Reserve Identification applies only if Extent is supported. This field must be zero if not supported. Check
with individual drive's Product Manual, Volume 1, section "SCSI Interface commands supported" (also see
paragraphs 5.35.1 and 5.35.2 in this volume).
[5]
See "Control byte," paragraph 4.2.6.
5.35.1
Logical Unit Reservation
If the Extent bit is zero, this command requests the entire 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until the reservation is superseded by another valid Reserve command from the initiator that made the reserva-
tion, released by a Release command from the same initiator, by a Bus Device Reset message from any initia-
tor, 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 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), an Inquiry command (which shall be executed), or a Request
Sense command (which shall be executed), the command is rejected with Reservation Conflict status.
5.35.2
Extent Reservation
The drive may not support Extent reservations, in which case this bit must always be zero. See individual
drive's Product Manual, Volume 1, section "SCSI Interface commands supported". Since the Reservation Iden-
tification byte and the Extent List Length are valid only for extent reservations, the drive ignores these fields if
extent reservations are not supported.
6
5
0
0
0
0
3rd Party
0 or 1 [2]
0
0
Reservation Identification [4]
0
0
Extent List Length (MSB) [3]
0
0
Extent List Length (LSB) [3]
0
0
SCSI Interface Product Manual, Rev. J
4
3
1
0
3rd Party Device ID [2]
0
0
0
0
0
0
0
0
2
1
1
1
Extent [3]
0
0
0
0
0
0
0
Flag [5]
Link [5]
0
0
0
0
0
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