Quantum DLT 2500, Product Manual

Page: 258 / 345

DLT2000 SCSI Interface
8-112 DLT2000/DLT2700 Cartridge Tape Subsystem
8.4.19 RESERVE UNIT (16h)
Bit
7 6 5 4 3 2 1 0
0 Operation Code (16h)
1 Logical Unit Number 3rdPty Third-Party Device ID RsvdD
Byte 2 Reserved
3 Reserved
4 Reserved
5 Unused Reserved Flag Link
Figure 8-71 RESERVE UNIT CDB
RESERVE UNIT reserves the specified drive for exclusive use by the requesting
initiator or for another specified SCSI device. The reservation remains in effect until
one of the following conditions is met:
•
The initiator that made the reservation sends another RESERVE UNIT command.
•
The drive is released by RELEASE UNIT 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 with a sense key of UNIT ATTENTION on the next command
following the condition. It is not an error to issue RESERVE UNIT to a drive that is
currently reserved to the requesting initiator.
If the logical unit has previously been reserved by another initiator, 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. A RELEASE UNIT command issued by
another initiator is ignored by that reserved logical unit.
3rdPty
The third-party reservation option for RESERVE UNIT allows an initiator to reserve a
logical unit for another SCSI device. This option is intended for systems that use
COPY, and is implemented by the drive.
If the third-party (3rdPty) bit is zero, then the third-party reservation option is not
requested. If the 3rdPty bit is one, RESERVE UNIT reserves the logical unit for the