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

Paul Suhler Paul.Suhler at Quantum.Com
Thu May 29 16:50:58 PDT 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* "Paul Suhler" <Paul.Suhler at Quantum.Com>
*
There's a potential issue with this, which the media changer community
ran into with the PREVENT/ALLOW MEDIUM REMOVAL command.  If one of the
initiators issues a START UNIT and then dies, the count will never get
back to zero.  After the initiator recovers, it's unlikely that it will
remember that it has an outstanding START and needs to issue a STOP.
Cheers,
Paul
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Paul A. Suhler | Firmware Engineer | Quantum Corporation | Office:
949.856.7748 | paul.suhler at quantum.com
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-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Rao,
Santosh Ananth
Sent: Thursday, May 29, 2008 3:59 PM
To: Gerry.Houlder at seagate.com; t10 at t10.org
Subject: RE: Drive behavior issue when START STOP unit forces drive to
idle power condition
* From the T10 Reflector (t10 at t10.org), posted by:
* "Rao, Santosh Ananth" <santosh.rao at hp.com>
*
It would be worth exploring alternatives for the target device (either
individual JBOD drives or array controllers) to track the number of
START UNITs received from individual I-T-L nexi (or hosts per logical
unit) and count down the corresponding STOP UNITs so that the drives
corresponding to the logical unit can be spun down when the STOP UNIT
count matches the START UNITs initially received.
Being able to track host closure of all active references to a logical
unit allows the target device to conserve power by spinning down the
drive or set of drives mapping to that logical unit when the last
application reference to the logical unit has been closed (volume group
de-activated on the host, filesystem unmounted, database shutdown, etc).
Thanks,
Santosh Rao
HP-UX Storage.
> -----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 1:55 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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