Unable to shutdown

[Kevin Oberman]

On Thu, Sep 1, 2011 at 2:01 AM,  <perryh at pluto.rain.com> wrote:
> Jeremy Chadwick <freebsd at jdc.parodius.com> wrote:
>> On Tue, Aug 30, 2011 at 11:04:43PM -0700, Kevin Oberman wrote:
>> > ... the standrad does not specify EXACTLY what triggers a
>> > transition from standby to ready (PM2 to PM0). Only that it is
>> > something that requires media access. A write does not
>> > necessarily require media access if you define "media" as the
>> > disk platter.
>>
>> You're correct -- "media access" could mean, literally, "accessing
>> the platter" OR it could mean "LBA read/write I/O".  Then comes
>> into question whether or not the drive returning something from
>> its on-board cache would count as "media access" or not.
>>
>> T13 should probably clarify on this point, and this is one I do
>> not have an answer for myself.  I strongly believe "media access"
>> means "LBA read/write I/O" and regardless if it's data that's in
>> the on-board cache on the disk or not.  I wonder if this behaviour
>> varies per drive model.
>
> Given a standard which is, shall we say, "open to interpretation",
> I think the liklihood approaches 100% that it has been interpreted
> differently by different manufacturers -- or even by different
> firmware authors within a single manufacturer.  I would be amazed
> if the behaviour did _not_ vary among drive models.

And, if you tell your firmware writers that they should look for any
technique that
reduces power consumption, I don't doubt that keeping the disk in
standby until there
was a reason to move data from write cache to disk would look good. I would hope
that they would not make a cache flush lie, but that used to be common
on old ATA
drives.
-- 
R. Kevin Oberman, Network Engineer - Retired
E-mail: kob6558 at gmail.com