James Phillips anti_spam256 at yahoo.ca
Fri Nov 13 20:15:56 UTC 2009

> Date: Thu, 12 Nov 2009 10:28:10 -0800 (PST)
> From: James Phillips <anti_spam256 at yahoo.ca>
> Subject: APM
> To: freebsd-questions at freebsd.org
> Message-ID: <784120.47330.qm at web65508.mail.ac4.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
> I realize the memory can't be shutdown without Hibernation
> support, but the disks can be spun down manually (using
> atacontrol):
> http://forums.freebsd.org/showthread.php?t=1012
> However, when I try to do that, I find that the disk wakes
> within 2 seconds of spinning down. I noticed that the
> spindowns are logged. Could the log being written be causing
> the drive to spin up again?
I initially set the time-out to 60 seconds, then 300 seconds in a vain attempt to see the actual power savings. With a 900 second time-out, the drive only spun down once in the past 12 hours.

It appears that syslogd can defer *one* log entry. Understandable, since you don't want to loose too many logs in a power failure.
tail /var/log/messages (trimmed entries from the 300 second time-out):
Nov 13 07:46:59 dusty kernel: ad4: Idle, spin down
Nov 13 07:46:59 dusty kernel: wakeup from sleeping state (slept 00:35:44)
Nov 13 07:47:01 ad4: request while spun down, starting.

It looks like the logging of the "spin down" woke up the sleeping system. Either that, or the computer did not know the actual spin-down time. The sleep time was reported to be 2144 seconds: 1244 seconds longer than the the set spin-down time (900 seconds).

If it was spun-down when I checked this morning, the difference was less than 3W. Though, the current drive (5400RPM) uses ~2 fewer watts than the old (7200 RPM) drive. I'm an not sure, since I replaced RAM, and installed an optical drive since measuring my base-line (with the old drive). 

My computer case has noise-dampening foam for the hard-disk. I can't hear if the drive is spinning over the inverter in the ADSL modem (9W) and the (quiet) fan noise from both the router (21W) and server. I can heard a "click" when it starts up, that is about it.


James Phillips

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