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Chapter 4 SCSI Commands
PERSISTENT RESERVE OUT Command (5Fh)
DLT-S4 Interface Reference Guide
219
PERSISTENT RESERVE OUT Command (5Fh)
4
PERSISTENT RESERVE OUT
is a 10-byte command used to reserve a
logical unit for exclusive or shared use of an initiator. The command is
used with the
PERSISTENT RESERVE IN
command.
Initiators that perform
PERSISTENT RESERVE OUT
actions are identified
by a Reservation Key the application client assigns. The application client
uses the
PERSISTENT RESERVE IN
command to identify which other
initiators within a system hold conflicting or invalid persistent
reservations and uses the
PERSISTENT RESERVE OUT
command to
preempt those reservations, if necessary.
Since the bus reset of
TARGET RESET
or other global action does not reset
persistent reservations, they can be used to enact device sharing among
multiple initiators.
The
PERSISTENT RESERVE OUT
and
PERSISTENT RESERVE IN
commands provide the means for resolving contentions in multiple-
initiator systems with multiple port targets. By using the Reservation Key
to identify persistent reservations, it is possible to determine which ports
hold conflicting persistent reservations and to reclaim these reservations
from failing or “greedy” initiators.
EX_AC_RO
The Exclusive Access – Registrants Only (EX_AC_RO) bit is set to one, indicating
that the device server supports the Exclusive Access – Registrants Only persistent
reservation type.
WR_EX_RO
The Write Exclusive – Registrants Only (WR_EX_RO) bit is set to one, indicating
that the device server supports the Write Exclusive – Registrants Only persistent
reservation type.
EX_AC
The Exclusive Access (EX_AC) bit is set to one, indicating that the device server
supports the Exclusive Access persistent reservation type.
WR_EX
The Write Exclusive (WR_EX) bit is set to one, indicating that the device server
supports the Write Exclusive persistent reservation type.
EX_AC_AR
The EX_AC_AR bit is set to zero, indicating that the device server does not
support the Exclusive Access – All Registrants persistent reservation type.
Field
Description