Quantum 10K II - Manual (Page 190)

SCSI Description
Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives 5–123
5.19 PERSISTENT RESERVATION OUT Command (5Fh)
The PERSISTENT RESERVATION OUT command is a 10-byte command used to
reserve a logical unit or an extent within a logical unit for the exclusive or shared
use by an initiator. The command is used in conjunction with the PERSISTENT
RESERVATION IN command; it is not used with the RESERVE and RELEASE
commands.
Persistent reservations conflict with reservations made via the RESERVE command.
Initiators that perform PERSISTENT RESERVATION OUT actions are identified by
a reservation key assigned by the application client. The client may use the
PERSISTENT RESERVATION IN command to identify which other initiators
within a system hold conflicting or invalid persistent reservations and use the
PERSISTENT RESERVATION OUT command to preempt those reservations if
necessary.
Note that since persistent reservations are not reset by the TARGET RESET task
management function or other global actions, they can be used to enact device
sharing among multiple initiators. The PERSISTENT RESERVATION OUT and
PERSISTENT RESERVATION IN commands provide the means for resolving
contentions in multiple-initiator systems with multiple port target. By using the
reservation key to identify persistent reservations, it is possible to determine which
ports hold conflicting persistent reservations and to take over such reservations from
failing or “greedy” initiators.
The figure below illustrates the format of the PERSISTENT RESERVATION OUT
command; the table that follows explains the data fields of the command.
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation Code (5Fh)
1 Reserved Service Action
2 Scope Type
3 - 6 Reserved
7 – 8
(MSB)
Parameter List Length (18h)
(LSB)
9 Control
Figure 5–54 PERSISTENT RESERVATION OUT Command Descriptor Block — Data
Format