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

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Thu May 29 13:54:33 PDT 2008


* 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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