Quantum DLT1/VS80 SCSI, Interface Manual

Page: 150 / 182

Chapter 4: SCSI Commands
4-108 July 2004 81-81276-01 Rev A01
4.19 RESERVE UNIT (16h)
The RESERVE UNIT command reserves the specified tape drive for the exclusive use of the
requesting initiator or for another specified SCSI device. The reservation remains in effect until one of
the following conditions occurs:
•
The initiator that made the reservation sends another RESERVE UNIT command.
•
The same initiator releases the tape drive with the RELEASE UNIT command.
•
The tape drive receives a BUS DEVICE RESET message from any initiator.
• A hard reset occurs.
The occurrence of the last two conditions is indicated by the tape drive returning a CHECK
CONDITION status with a 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 tape drive that is currently
reserved by the requesting initiator.
Figure 4-70. RESERVE UNIT (16h) Command Descriptor Block — Data Format
If another initiator has previously reserved the logical unit, the target returns a RESERVATION
CONFLICT status.
If, after the tape drive has honored the reservation, any other initiator attempts to perform any
command except INQUIRY, REQUEST SENSE, or RELEASE UNIT, the tape drive rejects the
command with a RESERVATION CONFLICT status. A reserved logical unit ignores a RELEASE
UNIT command issued by another initiator.
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation Code (16h)
1 Logical Unit Number 3rd Pty Third Party Device ID Rsv’d
2 - 4 Reserved
5 Unused Reserved Flag Link