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SCSI Commands
5-156 Quantum DLT 7000 Tape System
RESERVE UNIT Command (16h) (continued)
A reservation via the RESERVE UNIT command remains in effect until one of
the following conditions is met:
• The initiator that made the reservation sends another RESERVE UNIT
command.
• The tape drive is released via a RELEASE UNIT command from the same
initiator.
• A BUS DEVICE RESET message is received from any initiator.
• A hard reset occurs.
The occurrence of the last two conditions is indicated by the drive returning a
CHECK CONDITION status, sense key of UNIT ATTENTION on the next
command following the condition. It is not an error to issue a RESERVE UNIT
command to a drive that is currently reserved by the requesting initiator.
If another initiator has previously reserved the logical unit, the target returns a
RESERVATION CONFLICT status.
If, after honoring the reservation, any other initiator attempts to perform any
command except INQUIRY, REQUEST SENSE, or RELEASE UNIT, the
command is rejected with a RESERVATION CONFLICT status. That logical
unit ignores a RELEASE UNIT command issued by another initiator.
An initiator that holds a current reservation may modify that reservation (for
example, to switch third parties) by issuing another RESERVE UNIT command
to the tape drive.
Medium Changer Considerations for RESERVE UNIT Command
The optional Element Reservation feature defined for Medium Change devices as
described in the ANSI SCSI-2 specification is not supported. The RESERVE
command is defined the same as for the tape drive. The whole loader unit may be
reserved. This is separate from a reservation of the tape drive.
The RESERVE / RELEASE commands operate on a LUN basis. The Medium
Changer and the tape drive are generally handled as different devices. In the case
of a reserved drive LUN, a MOVE MEDIUM command issued to the Medium
Changer LUN cannot insert or remove a tape cartridge to or from a tape drive
unless the tape drive is reserved by the same initiator.