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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.