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

Rao, Santosh Ananth santosh.rao at hp.com
Thu May 29 15:59:25 PDT 2008


* 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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