On Thu, Sep 1, 2011 at 2:01 AM, <per...@pluto.rain.com> wrote: > Jeremy Chadwick <free...@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: kob6...@gmail.com _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
