MODE SELECT SP bit question - UPDATED

Gerry Houlder gerry.houlder at seagate.com
Fri Jan 28 13:32:28 PST 2011


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1101286_f.htm">HTML-formatted message</a>

i interpret the condition for returning SAVING PARAMETERS NOT SUPPORTED as
"the drive doesn't save any mode parameters". If even one mode parameter is
saved, the this error should not be returned.
On Fri, Jan 28, 2011 at 11:48 AM, Kevin D Butt <kdbutt at us.ibm.com> wrote:
> All,
>
> I was just surprised by one of my engineers telling me that the SP bit in
> the MODE SELECT command set to one indicates that ALL saveable mode
> parameters - not just those sent in this MODE SELECT command - are supposed
> to be saved.	I thought it meant to save the saveable parameters of those
> sent in this MODE SELECT command.  The text in SPC-4r29 states:
> <<An SP bit set to one specifies that the device server shall perform the
> specified MODE SELECT operation, and shall save
> to a nonvolatile vendor specific location all the saveable mode pages
> including any sent in the Data-Out Buffer.>>
>
> When I read this, I see the "including any sent in the Data-Out Buffer" and
> I have to conclude that my engineer is correct.
>
> His statement is, "In mode select, if SP=1 it seems like SPC explicitly
> indicates that all pages which are saveable (even if they were not sent in
> the mode select parameter data) shall be saved.  This means
> current->non-volatile memory for all saveable parameters.  Seems a bit bad
> from an application perspective (don't know who changed them and when), and
> a bit tough to do from a code perspective (need to process all saveable
> parameters/pages from current."
>
> Are we interpreting this correctly and should this be made more clear?
>
> In a related question, under MODE SENSE
> <<
> *6.11.5 Saved values*
> A PC field value of 11b requests that the device server return the saved
> values of the mode parameters. Mode
> parameters not supported by the logical unit shall be set to zero. If saved
> values are not implemented, the
> command shall be terminated with CHECK CONDITION status, with the sense key
> set to ILLEGAL REQUEST, and
> the additional sense code set to SAVING PARAMETERS NOT SUPPORTED.
>
> The method of saving parameters is vendor specific. The parameters are
> preserved in such a manner that they are
> retained when the device is powered down. All saveable mode pages should be
> considered saved when a MODE
> SELECT command issued with the SP bit set to one has completed with a GOOD
> status or after the successful
> completion of a FORMAT UNIT command.
> >>
>
> How is the above to be interpreted?  Is SAVING PARAMETERS NOT SUPPORTED
> intended to be returned only if the device does not support any parameters
> or is it intended to be returned if the requested page does not support any
> saveable parameters? If it is intended to be returned if the requested page
> does not support any saveable parameters, then what is the behavior on 3F
> (return all pages)?
>
> Next, the statement "...or after the successful completion of a FORMAT
> UNIT command" seems to me to be an SBC specific statement and should have
> a cross reference to SBC (and whatever other device type is appropriate).
>
> Kevin D. Butt
> SCSI & Fibre Channel Architect, Tape Firmware
> Data Protection & Retention
> MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
> Tel: 520-799-5280
> Fax: 520-799-2723 (T/L:321)
> Email address: kdbutt at us.ibm.com
> http://www-03.ibm.com/servers/storage/



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