Quantum DLT1/VS80 SCSI, Interface Manual

Page: 151 / 182

DLT1/VS80 SCSI Interface Guide
81-81276-01 Rev A01 July 2004 4-109
4.19.1 Medium Changer Considerations
The optional Element Reservation feature defined for Medium Changer tape drives in SCSI-2 is not
supported. The RESERVE command is defined the same as for the tape drive. The entire loader device
can be reserved. This is distinct from a reservation of the tape drive.
The RESERVE/RELEASE commands operate on a LUN basis. The medium changer and tape drive
are generally handled as different devices. In the case of a reserved tape drive LUN, a MOVE
MEDIUM command issued to the loader LUN cannot insert/remove a data cartridge in the tape drive
unless the same initiator has reserved the tape drive.
Table 4-62.
RESERVE UNIT (16h) Command Descriptor Block — Field Descriptions
Field Name Description
LUN Logical Unit Number. The target ignores this field. Only an IDENTIFY message
can change the LUN.
3rd Pty Third Party. The third-party reservation option for RESERVE UNIT allows an
initiator to reserve a logical unit for another SCSI device. This tape drive
implements this option, which is intended for systems that perform copy
operations.
When set to 0, the 3rdPty bit does not request the third-party reservation option.
When set to 1, RESERVE UNIT reserves the logical unit for the SCSI device
specified in the Third-Party Device ID field. The tape drive preserves the
reservation until any one of four conditions occurs (see the first paragraph of
“RESERVE UNIT (16h)” on page 4-108 ). The tape drive ignores any attempt
made by any other initiator to release the reservation and returns a GOOD status.
An initiator that holds a current reservation can modify that reservation (for
example, to switch third-parties) by issuing another RESERVE UNIT to the tape
drive.
Third Party Device ID This field identifies the SCSI device to be reserved.