Reference Guide

Chapter 4 SCSI Commands
RESERVE UNIT Command (16h)
DLT-S4 Interface Reference Guide 321
Figure 161 RESERVE UNIT
Command Data — Field
Descriptions
A reservation with the RESERVE UNIT command remains in effect until
one of the following conditions is met:
• Another valid
RESERVE UNIT command from the initiator holding
the reservation supersedes it.
•A
RELEASE UNIT command from the same initiator releases it.
• A Logical Unit reset request from any initiator releases it.
• A reset condition releases it.
The occurrence of the last two conditions is indicated by the drive
returning a
CHECK CONDITION status, Sense Key set to 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 drive, the drive returns a
RESERVATION CONFLICT status.
If, after honoring the reservation, any other initiator attempts to perform
any command that is subject to reservations, the drive rejects the
command with a
RESERVATION CONFLICT status. That drive 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 drive.
Field Description
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.
When set to 1, the drive is reserved for the SCSI device whose ID appears in the Third Party
Device ID field. The drive ignores any attempt made by any other initiator to release the
reservation and returns a GOOD status.
When set to 0, no third-party reservation is requested and the drive is reserved for the
initiator that issued the CDB.
Third Party
Device ID
If 3rdPty is set to 1, indicating that an initiator has reserved the drive for another SCSI device,
this field contains the ID number of the SCSI device for which the reservation was made.