Fujitsu M2488 manual Reserve Unit Operation

M2488 PRODUCT GUIDE TAPE UNIT SCSI COMMANDS

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the reservation is superseded by another valid RESERVE UNIT command from the initiator that the device is currently reserved for,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it is superseded by another valid RESERVE UNIT command from the initiator that made the third-party reservation,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 4-113