4-3.25.2 Reserve Unit Operation - Fujitsu M2488 Product Manual

M2488 PRODUCT GUIDE
4-3.25.2 RESERVE UNIT Operation
This command will always cause a synchronization unless:
The device is operating in Buffered Mode 1, wherein different initiators may have data in the
buffer at the same time, or
A third-party reservation is being requested where the 3rd Party Dev ID is that of the initiator
which currently has write data in the buffer.
This command requests that the entire logical unit be reserved for the exclusive use of the initiator
until:
the reservation is superseded by another valid RESERVE UNIT command from the initiator
that the device is currently reserved for,
the unit is released by a RELEASE UNIT command from the initiator that made the reserva-
tion,
a hard reset condition occurs,
a BUS DEVICE RESET message is received from any initiator, or
a power on cycle occurs.
The reservation is not granted if the logical unit is reserved by another initiator. It is permissible
for an initiator to issue a RESERVE UNIT command to a logical unit that it has already reserved.
If the logical unit is reserved for another initiator, the target returns RESERVATION CONFLICT
status.
If, after honoring the reservation, any other initiator tries to perform any command on the reserved
logical unit other than an INQUIRY, REQUEST SENSE or RELEASE UNIT command, then the
command is rejected with RESERVATION CONFLICT status. A RELEASE UNIT command is
ignored by returning GOOD status without altering any reservations, if received from an initiator
other than the one reserving the initiator.
The initiator will receive a BUSY (instead of a RESERVATION CONFLICT) status if the reserved
device is in the process of executing a command for the initiator or third-party device that holds
the reservation. The logical unit receiving the commands is checked for activity in progress before
being checked for reservation rights. If the reserved logical unit was not busy with a command for
the device that holds the reservation rights, then other initiators' commands will be rejected with
the RESERVATION CONFLICT status.
If an initiator attempts to make a third-party reservation for itself (i.e. the 3rdParty Dev ID field
has the same value as the ID of the initiator issuing the command), a CHECK CONDITION status
will be returned with sense data indicating ILLEGAL REQUEST/INVALID FIELD IN CDB.
The target preserves a successful third-party reservation until:
it is superseded by another valid RESERVE UNIT command from the initiator that made the
third-party reservation,
it is released by the initiator that made the third-party reservation,
a BUS DEVICE RESET message is received from any initiator, or
a hard reset condition occurs.
While a third party reservation is active, the target ignores any attempt to release the reservation
made by any other initiator.
April 1997 CG00000-011503 REV. A
TAPE UNIT SCSI COMMANDS
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