Reserve - HP C2488A Technical Reference Manual

Reserve
The RESERVE command is used to reserve logical units for the use of the Initiator. With
third-party reservation, the logical units may be reserved for another specified SCSI device.
The RESERVE and RELEASE commands provide the basic mechanism for contention
resolution in multiple-Initiator systems.
Reserve Command Descriptor Block (COB)
Bit
Byte
7
I
6
I
I)
I
4
I
3
I
2
I
1
I
0
00 Opcode
=
I6H
01 Logical Unit Number
J
3RDPTY
J
Third Party Device ID
J
XTNT
=
0
02
Reservation Identification
=
00
03-04
(MSB=03) Extent List Length
=
00 (LSB=04)
01)
Control Byte
3RDPTY (Third-Party). A 3RDPTY bit set to one (1) indicates that the reservation is being
made on behalf of another bus device (the third party). When 3RDPTY is set to zero (0),
third-party reservation is not requested.
Third Party Device ID. This field indicates the identity of the third party. The reservation
can only be released by the party that made the reservation.
When a third-party reservation is made, the mode parameters of the reserving Initiator will be
copied to the mode parameters of the third party. This will cause Unit Attention to the third
party with a Sense Key of UNIT ATTENTION (6) and an Additional Sense Code of MODE
SELECT PARAMETERS CHANGED (2AH).
XTNT (Extent Reservation). With the XTNT bit set to zero (0), this command will
request that the entire logical unit be reserved for the exclusive use of the Initiator until the
reservation is superseded by another valid RESERVE command froni the same mitiator that
made the reservation or until 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 will not be granted if the logical unit is reserved by another Initiator.
It will be permissible for an Initiator to reserve a logical unit that is currently reserved by
that Initiator. With XTNT set to zero (0), The Reservation Identification and the Extent List
Length fields will be ignored.
If the logical unit is reserved for another Initiator, the target will respond by returning a
RESERVATION CONFLICT status. . ...
Once a reservation is installed, the reserved logical unit is available only to the Initiator that
issued the RESERVE command, or a specified optional third party. If any other Initiator
attempts to perform a command on the reserved logical unit the command will be rejected
with RESERVATION CONFLICT status. Exceptions are the RELEASE command, which
will be ignored by the target, and the INQUIRY command, which will be executed.
A-48 SCSI Command Descriptions DRAFT
1/18/93 09:58