Drive behavior issue when START STOP unit forces drive to idle power condition

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Thu Jun 5 07:38:08 PDT 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*
I looked at Power Condition codes Ah and Bh. The description for these
codes is "force xxx condition timer to zero". I interpret this to mean
setting the associated timer to 0 and the timer value stays set to zero.
The effect of this is to force the device to that idle mode immediately
after the completion of every command. Everyone I talk to thinks this
behavior is horrible (big performance hit, extra wear on mechanical parts,
more power consumption than staying in active condition if commands arrive
at intervals of 1 second apart or less).
If you are saying that the intent of these two condition codes is to force
the drive immediately to a particular power condition but leave all timers
on mode page 1Ah active, same timer value as currently set in the timers,
and the timers will restart after completion of the next command that
changes power conditon to active then I would concede this does what I
want. The current description sure doesn't say this, however.
Does anyone actually implement these options? If so, how did you interpret
the behavior?
I see the current behavior description of these two options as completely
undesireable.
(a) I would propose obsoleting these if others feel the same way and
implementing a new bit to achieve the behavior I want (a reply from Fred
Knight suggested this).
(b)  I could also redefine power condition options Ah and Bh to do what I
want if no one has actually implemented them as described today. Since this
would require canvassing the industry for implementions first, this seems
more risky.
	     "Penokie, George"						   
	     <George.Penokie at l						   
	     si.com>							To 
	     No Phone Info	       "Gerry.Houlder at seagate.com"	   
	     Available		       <Gerry.Houlder at seagate.com>,	   
				       "t10 at t10.org" <t10 at t10.org>	   
									cc 
	     06/02/2008 05:10						   
	     PM 						   Subject 
				       RE: Drive behavior issue when START 
				       STOP unit forces drive to idle	   
				       power condition			   
Gerry,
The ability to use the Start/Stop Unit command in cooperation with the
Power Condition mode page is already defined in the Start/Stop Unit
command. The Power Condition field codes Ah and Bh allow the application to
force a change to a different power condition without disabling the timers.
In addition, if the application does use the Start/Stop Unit command to
control the power conditions manually using Power Conditions 1h, 2h, or 3h
it can switch over to using the Power Condition mode page any time by
issuing a Start/Stop Unit command with the Power Condition set to 7h.
Bye for now,
George Penokie
LSI Corporation
3033 41st St. NW
Suite 100
Rochester, MN 55901
507-328-9017
george.penokie at lsi.com
-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of
Gerry.Houlder at seagate.com
Sent: Thursday, May 29, 2008 3:55 PM
To: t10 at t10.org
Subject: Drive behavior issue when START STOP unit forces drive to idle
power condition
* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*
While working on my additional idle power conditions proposal (08-184) I
encountered this issue with using START STOP UNIT command to force the
drive to idle mode.
Situation: initiator sends START STOP UNIT command that forces drive to
idle power condition. As defined today, this action disables any timers on
the Power Condition Mode page (page 0x1A) that happen to be enabled. Later
a media access command causes the drive to transition to active state to
process the command. Since the timers are disabled, the drive will stay in
active state until another START STOP UNIT command is sent.
Problem: With multi-initiator systems, will all the initiators know to send
a START STOP UNIT command to put the drive back to idle to conserve power?
If not, a drive that at least one initiator thinks is in an idle power
condition (conserving power) may actually be in active power condition for
long periods of time.
Possible solution: change the START STOP UNIT command behavior so that
sending the command causes the drive to transition immediately to the
requested power condition but don't disable the timers. Then if the drive
goes to active power condition to process a media access command, it will
still go to idle  power condition based on the timers. This would at least
limit the unnecessary active time of the drive to the values set in the
timers.
I'd like to hear what other companies think of this situation. Will drives
always be fully manged in a multi-initiator system so the stated problem
will not be an issue or should something be changed to limit the impact of
this issue? Are there existing implementations that use the current START
STOP UNIT behavior? If not, perhaps we can consider changing the behavior.
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