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Cc: dmagda@ee.ryerson.ca, freebsd-stable@freebsd.org, dart@es.net
Subject: Re: Unable to shutdown
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Jeremy Chadwick <freebsd@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.