Quantum ATL SuperLoader ATL, User Manual

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Chapter 3 Media Changer Commands
Persistent Reserve Out Command (5Fh)
Quantum ATL SuperLoader Software Interface Guide 101
Persistent Reserve Out Command (5Fh)
3
The PERSISTENT RESERVE OUT command is a 10-byte command
used to reserve a logical unit for the exclusive or shared use by an
initiator. The command is used in conjunction with the
PERSISTENT RESERVE 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
RESERVE OUT actions are identified by a reservation key assigned
by the application client. The client may use the PERSISTENT
RESERVE IN command to identify which other initiators within a
system hold conflicting or invalid persistent reservations and use
the PERSISTENT RESERVE 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 RESERVE OUT and PERSISTENT
RESERVE 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 that follows illustrates the format of the PERSISTENT
RESERVE OUT command; the table that follows explains the data
fields of the command.