TST bit logic error in SAM-2 specification

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Fri Apr 19 12:04:27 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*

 To para-phrase Rob's response, the standard requires the TST field to be
implemented as "one copy shared by all initiators" even if the target
implements separate copies of other mode parameters. Even on an
implementation that does separate copies of mode pages for each initiator,
this parameter and a number of other parameters must be implemented as
"shared by all initiators".

A target (or more correctly, a LUN) will not change the way it saves mode
pages based on this mode setting or any other mode page setting. It is too
difficult to implement (i.e., takes too much code space to handle both
cases) both methods in a target and allow an initiator to choose how it is
done. I would never assume a target will change this characteristic of its
behavior based on a mode page setting -- the choice will be based on a
compile time option.

In summary: the system controls this target behavior (if it cares) by
specifying the mode page behavior in a purchase specification, not by a
mode page setting. Most systems are designed to tolerate the "one copy
shared by all initiators" case and this will also tolerate the "copy per
initiator" case also.

The wording of the sense code is "MODE PARAMETERS CHANGED" because there
might be only one shared parameter changed, multiple shared parameters
changed, or even could mean a MODE SELECT was done that might have changed
a mode setting (in this case there might not have been an actual mode
parameter change anywhere). If the initiator cares, it has to check all the
mode pages it cares about to see if something has changed. All of these
cases (not sure - could be zero, one, more than one) will report the same
ASC/ASCQ.



                                                                                              
                    "Mark Brown"                                                              
                    <mkbrown_san at ho        To:     t10 at t10.org                                
                    tmail.com>             cc:                                                
                    Sent by:               Subject:     RE: TST bit logic error in SAM-2      
                    owner-t10 at t10.o        specification                                      
                    rg                                                                        
                                                                                              
                                                                                              
                    04/19/02 11:43                                                            
                    AM                                                                        
                                                                                              
                                                                                              




* From the T10 Reflector (t10 at t10.org), posted by:
* "Mark Brown" <mkbrown_san at hotmail.com>
*
Excuse me I did not see this message until just now.  Thank you for
responding.  My response:

The implication of the Unit Attention sent to all initiators is that some
major operational change has occurred at the Target. This implies that the
TST bit enables and disables the maintenance of Mode Page state information
on a per initiator basis.
This further indicates that, as I have suggested, the TST bit has more
power
than simply to enable multiple queues for Abort Task Set and Clear Task Set
purposes, but actually has been given broad operational powers enabling the
maintenance of State information by the Device Server on a per initiator
basis (both Request Sense information and now Mode Page information).

Let's put it this way:  I do not believe that a functionality as pervasive
in effect inside the Device Server as well as the Task Manager  as
maintaining separate Mode Pages per initiator could be specified without an
explicit ability to Enable and Disable it, let alone to interrogate its
current setting.  Therefore, it is fair to assume that that portion of the
SPC-3 8.4.6 text is stating that the TST bit enables/disables multiple mode
pages.
If TST does not enable/disable multiple mode pages, some other bit should.

If the intent is the opposite then at the least the text should read:
"...shall reflect in all initiator mode pages the  new state of the TST
field  selected by...", or
"...the state of the TST field, if changeable, shall reflect in all
initiator mode pages the selection by..."

The plural ASC "MODE PARAMETERS CHANGED" also implies more than just the
TST
field has changed,
again indicating that the last initiator's whole Control page (containing
the TST field) just became the Control page for all initiators. And that
subsequent changes to other pages by the same or other initiators would
have
the same effect on the other initiators.

Mark Brown, Micronet Software

>From: "Elliott, Robert" <Robert.Elliott at COMPAQ.com>
>To: <t10 at t10.org>
>Subject: RE: TST bit logic error in SAM-2 specification
>Date: Wed, 17 Apr 2002 17:56:49 -0500
>
>* From the T10 Reflector (t10 at t10.org), posted by:
>* "Elliott, Robert" <Robert.Elliott at COMPAQ.com>
>*
> > -----Original Message-----
> > From: Mark Brown [mailto:mkbrown_san at hotmail.com]
> > Sent: Wednesday, April 17, 2002 4:15 PM
> > Subject: TST bit logic error in SAM-2 specification
> >
> > ...
> > Furthermore, SPC-3 8.4.6 implies that Mode Pages may be maintained
> > separately for each initiator when TST = 001b, though this
> > portion of the text is ambiguous as to whether TST requires
> > and/or enables this  functionality.
>
>The reference to mode pages in 8.4.6 means there is only one
>TST value per logical unit - it is shared -  regardless of
>whether the other fields in the Control mode page are shared.
>If the Control mode page is not shared and one initiator
>changes the TST field, all the others get a unit attention.
>This is not true of the other fields.
>
>This was one of the reasons the text was reworded in revision 4;
>see 02-016r1.
>
>---
>Rob Elliott, Compaq? Server Storage
>Robert.Elliott at compaq.com
>
>*
>* For T10 Reflector information, send a message with
>* 'info t10' (no quotes) in the message body to majordomo at t10.org


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