SAM-2 status precedence - RESERVATION CONFLICT vs. CHECK CONDITON/UNITATTENTION/POWER ON OCCURRED

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Mon Mar 25 15:38:59 PST 2002


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

One little nuance here for the persistent reservation case -- after power
on the drive doesn't know whether there is a conflicting presistent
reservation because it hasn't been able to consult with the table stored on
the disk (the non-volatile memory) yet. That is why there is a section of
the persistent reservation model addressing the behavior after power on and
before the drive is sure whether or not there is a reservation.

Technically the drive doesn't know there is a conflict, so I think this
case is OK. When the drive gets to the state where it knows there is a
conflict, then the RESERVATION CONFLICT status will occur.

This gets foggier if the target is actually storing the persistent
reservation table in local NVRAM that actually is available right after
power on. In this case an Inquiry or Request Sense would execute (they are
allowed through reservations and unit attentions) but a Test unit Ready
command would get a RESERVATION CONFLICT even if it was the first command
sent to the target. The behavior change will probably occur when a small
amount of NVRAM gets cheap enough. Maybe Rob is saying he doesn't want to
see this behavior change -- that unit attentions (or at least the power on
or reset occured unit attention, or maybe Not Ready sense key as well)
should be reported in preference to RESERVATION CONFLICT?



                                                                                                
                    "Elliott, Robert"                                                           
                    <Robert.Elliott at C        To:     <t10 at t10.org>                              
                    OMPAQ.com>               cc:                                                
                    Sent by:                 Subject:     SAM-2 status precedence - RESERVATION 
                    owner-t10 at t10.org        CONFLICT vs. CHECK CONDITON/UNIT ATTENTION/POWER   
                                             ON OCCURRED                                        
                                                                                                
                    03/25/02 01:42 PM                                                           
                                                                                                
                                                                                                




* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert" <Robert.Elliott at COMPAQ.com>
*
SAM-2 requires that RESERVATION CONFLICT status always have priority
over CHECK CONDITION status:

"5.3.2 Status precedence
 If more than one condition applies to a completed task, the report
 of a BUSY, RESERVATION CONFLICT, ACA ACTIVE or TASK SET FULL
 status shall take precedence over the return of any other status
 for that task."

However, after power up, most targets with a persistent reservation
stored in non-volatile memory return CHECK CONDITION status to report
a unit attention with an additional sense code of POWER ON OCCURRED
rather than report the RESERVATION CONFLICT status.

Depending on how you interpret "more than one condition applies"
this violates the SAM-2 precedence rule.

Also, SPC-3 describes how CHECK CONDITION/NOT READY is supposed
to be returned after power on until the persistent reservation
information has been loaded.

How should the SAM-2 text change to fix this?
a) change "shall" to "should"
b) add "except for a CHECK CONDITION status reporting a
UNIT ATTENTION sense key with an additional sense code with
an ASC set to 29h, or a CHECK CONDITION status reporting
a NOT READY sense key"
c) other suggestions

---
Rob Elliott, Compaq? Server Storage
Robert.Elliott at compaq.com


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