DS bit usage in log page 00

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Fri Jun 19 13:40:40 PDT 2009

* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
I am posting this to SCSI reflector because it turns out that moving the DS
bit from the parameter control byte to the page code byte may cause
backwards compatibility issues for some companies. The example discussed
thi these emails is the Supported Log Pages page, where the page code byte
would change from 0x00 to 0x80 if the DS bit was set for this page. Setting
this bit seems like the right thing to do for this page (it is described as
being undefined for LOG SELECT, so it seems not to qualify to have any
savable parameters) but software that tries to retrieve this page may be
confused by the result.
Pages that have savable parameters should not see an issue (the DS bit = 0,
so will look the same as before).
I ask that companies evaluate whether this item will be a problem for their
software that reads up log pages. I would like to hear opinions at the July
T10 meeting from companies on this issue.
	     "Elliott, Robert						   
	     (Server Storage)"						   
	     <Elliott at hp.com>						To 
	     No Phone Info	       "Gerry.Houlder at seagate.com"	   
	     Available		       <Gerry.Houlder at seagate.com>,	   
				       "roweber at ieee.org"		   
				       <roweber at ieee.org>, Mark Evans	   
	     06/19/2009 02:49	       <Mark.Evans at wdc.com>		   
	     PM 							cc 
				       RE: DS bit usage in log page 00	   
The history is:
1. Before SPC-3 letter ballot, log page byte 0 contained an 8-bit the PAGE
CODE field
2. In letter ballot, byte 0 bits 7:6 changed to Reserved per a Dell LB
comment that the CDBs only had 6-bit PAGE CODE fields.
3. At that time, each log parameter had its own DS bit
4. 05-242r2 (by Mark) made the parameter-specific bit DS bit obsolete and
created a new page-specific DS bit in byte 0 bit 7
The Supported Log Page page did not have conventional "log parameters" so
never had DS bits.
I think the Supported Log Pages log page (00h/00h) should always return
DS=0 to remain the same as it has always been.	The Supported Log Pages And
Subpages log page (00h/FFh) and Supported Subpages (xxh/FFh) log pages
should follow suit.
> -----Original Message-----
> From: Gerry.Houlder at seagate.com [mailto:Gerry.Houlder at seagate.com]
> Sent: Thursday, June 18, 2009 7:52 PM
> To: roweber at ieee.org; Mark Evans; Elliott, Robert (Server Storage)
> Subject: DS bit usage in log page 00
> Hi gang,
> I have noticed that log page 00 (the Supported Pages log page) has a
> statement that this log page is not defined for LOG SELECT, only for
> SENSE. Does this suggest that the DS bit for this page shall be set to
> 1?
> The definition for this bit suggests that this bit is mostly useful for
> SELECT. Should something be added to the log page 00 description
> defining
> the DS bit as set to 1 for this page?
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