X3T10/94-236: Addressability of TARGET RESET task management function

Bob Snively Bob.Snively at Eng.Sun.COM
Tue Nov 22 00:00:02 PST 1994

The following document revises a paper presented at the SCSI meeting.
The original paper proposed that TARGET RESET allow addressing to
entities below the first node in a hierarchically addressed device.
The members of the committee suggested that a separate function be
defined to perform this operation.  The suggested name was 
LOGICAL UNIT RESET.  This paper proposes that modified function, although I
would cheerfully change back to the original definition.


To:		X3T10

From:		Bob Snively
		Sun Microsystems Computer Company
		Mail Stop UMPK 12-204
		2550 Garcia Ave,
		CA 94043-1100
		(415) 786-6694

Date:		November 22, 1994

Subject: 	Addressability of TARGET RESET task management function

The development of hierarchically organized address structures as described 
in the SCC document (X3T10/1047D, Revision 3) requires the addition of a task 
management function that can selectively perform a reset for a target below 
the top level of the hierarchy.  To meet this requirement a LOGICAL UNIT RESET 
task management function is proposed as an addition to the SAM document 
(X3T10/994D, Revision 16).  This document proposes architectural concepts 
and an implementation for the LOGICAL UNIT RESET function and proposes 
wording additions to SAM to incorporate the new function.

Architectural Concepts:

At present, the TARGET RESET function acts on all logical units attached 
to the SCSI port.  In the case of hierarchically organized address structures, 
targets actually exist in the address space defined by the logical unit 
number.  LOGICAL UNIT RESET is defined to perform the TARGET RESET function 
on those targets and logical units existing in the LUN address space.  The 
LOGICAL UNIT RESET function addressed to one of those targets or logical 
units does not influence other peer units in the hierarchy and resets the 
addressed unit and all targets and logical units below the addressed unit 
in the hierarchy.

Proposed Implementation:

The object address for the LOGICAL UNIT RESET contains the logical unit 
number of a destination logical unit.  The logical unit and all dependent 
logical units will be reset.  SAM must be modified in the following manner.

Modifications to SAM:

Section 7 should have the following text added between the descriptions of 

"LOGICAL UNIT RESET (Logical unit number||) - Reset the specified logical 
unit and all targets and logical units hierarchically addressed from the 
logical unit.  All tasks in all task sets for all affected logical units 
are reset.  All hierarchically addressed SCSI devices shall support this 
function.  For SCSI targets not having hierarchical addressing, implementation 
of this function is a logical unit option."

The following new section 7.n is added between the present section 7.4 and 7.5:


Function Call:

Service Response = 
		LOGICAL UNIT RESET (Logical unit identifier||)


This function shall be supported by all SCSI targets that support hierarchical 
address structures.  The function is optionally supported by other SCSI targets.

The logical unit addressed by the logical unit identifier is reset according 
to the rules of the TARGET RESET function.  That logical unit and all lower 
logical units in the hierarchy are reset.  Peer logical units and logical 
units above the addressed logical unit are not affected by the 

Before returning a Function Complete response the addressed logical unit 
shall perform the hard reset functions specified in clause 6.6.6 and shall
create a unit attention condition in all affected logical units for all 
initiators as specified in clause 6.6.5.

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