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Commands164
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 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)
1 Reserved (0) 3rd Pty(0) Third-Party Device ID (0) Rsvd(0)
2
Reserved (0)
4
5 Control
3rdPty This is always zero because third-party reservation is not supported.
Third-Party Device ID This is always zero because third-party reservation is not supported.