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ACL 4/52 Software Interface Guide
Document 6211225-03
Version 3.0
3-56
SCSI Interface
Table 36: Reserve
Command
Logical Unit Number
The Logical Unit Number must always be 0. This field indicates
which logical unit the command should be sent to.
3rdPty
and 3rd Party ID
The 3rd 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 library.
If the 3rd party (3rdPty) bit is zero, then the 3rd party reservation
option is not requested. If the 3rdPty bit is one, Reserve Unit
reserves the logical unit for the SCSI device specified in the 3rd
party device ID (3rd Party ID) field. The library preserves the
reservation until any one of the four conditions mentioned above
occurs. The library ignores any attempt made by any other initiator
to release the reservation and returns a Good status.
An initiator that holds a current reservation may modify that
reservation (for example, to switch third-parties) by issuing
another Reserve Unit to the library.
Element and Reservation ID
The Element field specifies whether this command is an Element
or Unit Release. If the value is one, the command will Release all
elements reserved by the requesting initiator, that were reserved
with the same Reservation ID value as this release attempt and that
meet 3rd party release requirements, if applicable. If the value is
zero, the command will Release a reservation placed on this unit
by the requesting initiator that meets 3rd party release
requirements, if applicable.
Bit/Byte
7
6
5
4
3
2
1
0
0
Operation Code (16h)
1
Logical Unit Number
3rdPty
3rd Party ID
Element
2
Reservation ID
3
(MSB)
Element List Length
(LSB)
4
5
Unused
Reserved (00h)
Flag
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