Date: Wed, 31 Aug 2011 20:23:00 -0700 From: Kevin Oberman <kob6558@gmail.com> To: perryh@pluto.rain.com Cc: dmagda@ee.ryerson.ca, freebsd-stable@freebsd.org, dart@es.net, freebsd@jdc.parodius.com Subject: Re: Unable to shutdown Message-ID: <CAN6yY1szj4t1_Ho--6VnhXe9ewjthTTin7auvJAgtem2o5_0aQ@mail.gmail.com> In-Reply-To: <4e5f49fa.2qH1H6gV7TIdZYiD%perryh@pluto.rain.com> References: <CAN6yY1s3x1ojxh-Dx9Ht=L8M4frohLXcMLNgz%2BzgtBCDodBdsg@mail.gmail.com> <uh78vqd9u8e.fsf@P142.sics.se> <4E5BF15F.9070601@es.net> <CAN6yY1u6ZshVZT2DwaQ2Et7Y1JvNA8q%2BFj5os4SmK4=7=Z77vg@mail.gmail.com> <f0ffdf9eccf14f42ee24f0982bb0fc4b.squirrel@webmail.ee.ryerson.ca> <20110830214832.GA87354@icarus.home.lan> <CAN6yY1upYKW9e3mmED11pTXk%2BVO1KduPy-boWTr7m9S42jUKWw@mail.gmail.com> <20110830234323.GA88936@icarus.home.lan> <CAN6yY1v%2ByqZTkX=XjAoLJWNuf%2Bz6OwR-s2sfdGuGk_RXwBK_VA@mail.gmail.com> <20110831071207.GA95960@icarus.home.lan> <4e5f49fa.2qH1H6gV7TIdZYiD%perryh@pluto.rain.com>
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On Thu, Sep 1, 2011 at 2:01 AM, <perryh@pluto.rain.com> wrote: > 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". =A0Then 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. =A0I 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. =A0I 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. =A0I 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. --=20 R. Kevin Oberman, Network Engineer - Retired E-mail: kob6558@gmail.com
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