Commands 141
Commands
RESERVE UNIT 16h/56h
This command enables the host to reserve the drive. Reserving a device is a
way of ensuring exclusive access to that device from a single initiator for the
period of the reservation.
Once reserved, the drive will execute commands received from the reserving
initiator or from the third-party initiator if the 3rd-Pty option has been selected.
Commands from other initiators will have
RESERVATION CONFLICT status
reported for them, apart from
INQUIRY, REQUEST SENSE, LOG SENSE, REPORT
LUNS
, REPORT DENSITY SUPPORT, READ BLOCK LIMITS and RELEASE UNIT.
The
INQUIRY, REQUEST SENSE, LOG SENSE, PREVENT/ALLOW MEDIUM
REMOVAL
(Allow=0), REPORT LUNS, READ BLOCK LIMITS and REPORT DENSITY
SUPPORT
commands are immune to the effects of a reservation and will
continue to execute for all hosts. The
RELEASE UNIT command will have GOOD
status reported for other hosts, but will have no effect on the reservation.
The 10-byte RESERVE UNIT command is supported by all drives. Its
functionality is the same as for the 6-byte command, but it also supports third-
party reservation.
The reservation will stay in effect until:
■ The reserving host sends another RESERVE UNIT command.
■ The reserving host sends a RELEASE UNIT command, clearing the
reservation.
■ A power-on, firmware upgrade or forced eject.
Pre-Execution Checks:
If the drive is reserved by some other host then reservation conflict status is
reported to the host.
Command Descriptor Block:
6-Byte
Illegal Field Deferred Error Unit Attention
7 6 5 4 3 2 1 0
0
Operation Code (16h)
