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

Knight, Frederick Frederick.Knight at netapp.com
Fri May 30 08:43:58 PDT 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* "Knight, Frederick" <Frederick.Knight at netapp.com>
*
There are 2 clear methods to manage power, and 1 less clear method.
1) totally automatic - set the mode page, and the drive does it all.
Transitions are automatic in and out of various power modes.
2) totally manual - the initiator sends START/STOP commands to put the
drive where it wants it (and it stays there).
3) a mix - set the mode page AND use the START/STOP commands.  This I
think is the less clear case.  Right now, it appears that sending a
START/STOP command turns off automatic mode and force you into manual
mode.  That was probably intended.
You probably want a new bit in the POWER CONDITION MODE PAGE to allow
case 3 to keep automatic mode enabled when you use the START/STOP
commands.  This keeps what is there working as it was probably
originally intended, and adds the new ability to use START/STOP for
temporary manual changes, but also keep the timers running so automatic
mode can continue to operate concurrently.
	Fred Knight
-----Original Message-----
From: Gerry.Houlder at seagate.com [mailto:Gerry.Houlder at seagate.com] 
Sent: Thursday, May 29, 2008 4:55 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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