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Command Specifications
3 - 38 C141-E167
Together with the RELEASE command, this command controls exclusive access to the logical unit
(IDD) under a multi-initiator environment.
The IDD is reserved by this command for the INIT which issued this command or for some other
SCSI device specified in the CDB.
The INIT which issues this command must notify the IDD of its own SCSI ID when the
SELECTION phase is executed.. When the INIT's ID cannot be specified, this command is
terminated with a CHECK CONDITION status (ILLEGAL REQUEST [=5] / Initiator's SCSI ID not
identified [=90-00]) without being executed. Also, the values specified in bytes 2 to 4 of the CDB
have no meaning and are disregarded, but it is preferable that the INIT specify X '00' in these bytes.
(1) Logical unit reserve function
This command reserves the entire IDD (logical unit) for use as a special SCSI device. The reserve state
established by this command is maintained until any one of the following conditions occurs.
1) The reserve condition is changed by the INIT that issued this command (Superseding Reserve).
2) Reserve is released by a RELEASE command from the INIT that issued this command.
3) A TARGET RESET message from any INIT.
4) A RESET condition.
5) Switching the IDD's power off or on.
When an IDD is reserved for any SCSI device, if this command is issued by an INIT that doesn't
have the "Reserve Right" for that IDD, this command is terminated with a RESERVATION
CONFLICT status. See item (3) concerning the "Reserve Right."
After the Reserved status is established, a command issued by an INIT other than the SCSI device that
reserved the IDD is rejected, except an INQUIRY, REQUEST SENSE or RELEASE command, and a
RESERVATION CONFLICT status is reported to the INIT that issued that command. The INQUIRY and
REQUEST SENSE commands are executed normally even when the IDD is reserved for use by another
SCSI device. Also, a RELEASE command is terminated with a GOOD status, but the release operation
specified in a RELEASE command issued to the IDD by a SCSI device which does not have the Reserve
Right is disregarded.
(2) Reserve right and third party reserve function
If the "3rd Pty" bit in byte 1 of the CDB is "0," the IDD is reserved by the INIT which issued this
command and that INIT has the Reserve right for the IDD.
If the "3rd Pty" bit is "1," the third party reserve function is specified. An INIT which specifies the
third party reserve function and issues this command can reserve the IDD for use by another SCSI
device. In this case, this command reserves the IDD for the SCSI device (called the third party
device) with the SCSI ID specified in the "3rd Pty Dev ID" field in byte 1 of the CDB. Even if the
IDD is reserved for another SCSI device using the third party reserve function the reserve right for
that ID resides with the INIT that issued this command. Therefore, in order to release that reserve
state, it is necessary for the INIT that issued this command to issue a RELEASE command (shown in
Section 3.1.13) with the third party release function specified. Also, the conditions for maintaining
the reserve state established by the third party reserve function are the same as in the case where the
third party reserve function is not used. (See item (1).)
Please note that since only 3 bits are defined for the "3rd Pty Dev ID" field, this command is valid
for the third party reserve function with respect to only SCSI devices with SCSI ID 7 to 0.