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Chapter 8 SCSI Commands
The SCSI Bus Address field is the SCSI Address of the Data Transfer Element
(Tape Drive) supported by the autoloader and specified by the Element Address.
The Logical Unit Number field is the Logical Unit Number in the Data Transfer
Element (Tape Drive) supported by the autoloader and specified by the Element
Address. The Tape Drive in the autoloader supports only LUN=0, therefore this
is always 0.
8.18. RESERVE Command (16h)
The RESERVE command is used to reserve the autoloader so that the host can
use it exclusively. The RESERVE and RELEASE commands provide a means
of avoiding races in multi-initiator environments.
Table 8.18.1 : RESERVE command
8.18.1. Logical unit reservation
When the Element bit is 0, the RESERVE command requests exclusive use of
the Unit by the host issuing the command until reservation is released. Release
of the reservation occurs as a result of:
1) Issue of a valid RELEASE command by the host that issued the RESERVE
command.
2) Issue of a BUS RESET message by any host.
3) A hard reset.
4) Power on cycle.
If another host issues a RESERVE command to the Unit or element while it is
reserved is not permitted. It is permitted for a host already holding a reservation
to reissue a reservation request to the Unit or element. When the Element bit is
0, the Reservation Identification and Element List Length are ignored.
When a Unit or Element in the autoloader is reserved by another host, the
autoloader returns the RESERVATION CONFLICT status.
If another host issues a command other than INQUIRY, REQUEST SENSE,
REPORT LUNS, PREVENT ALLOW MEDIUM REMOVAL, RESERVE, or
RELEASE after a reservation is confirmed, a RESERVATION CONFLICT
status is returned and command execution is excluded.
Bit
Byte
7
6
5
4
3
2
1
0
0
Operation code (16h)
1
Logical unit number(0h)
3rdPty(0)
Third party device ID(0)
Element
2
Reservation identification
3
(MSB)
Element list length
4
(LSB)
5
Control(0h)
