hard disk power down (was: Re: PowerTOP tool released; time to fix the wasted laptop power on fedora?)

[Thorsten Leemhuis]

On 13.05.2007 19:06, Arjan van de Ven wrote:
> On Sun, 2007-05-13 at 23:52 +1000, David Timms wrote:
>> Arjan van de Ven wrote:
>>> some of you already know that I've been working on getting Linux (and
>>> Fedora) to be a lot better about power usage on laptops by avoiding
>>> spurious wakeups and context switches and such (look at the "wakeup" bug
>>> in fedora bugzilla ;).
>> ...
>> Would this tool help one in tracing the cause of disk accesses in an 
>> otherwise inactive/idle notebook. It seems to be about every 3 seconds 
>> or so that the hard disk LED lights. This must make it impossible for 
>> the hard drive to get powered down - and save power.
> I've gotten this request a few times now; I'll be looking into this for
> version 2.0; I'd think it would be possible with blktrace but I need to
> look into the details (don't want this tracing to spoil any other
> measurements ;)

Just wondering: does Fedora spin down the hard disk by default? It
doesn't afaics and it's not easily user-configurable either afaik.

Gnome-power-manager sounds like the proper place to control if the hard
disk gets powered down; but well, seem Richard got burned when he tried
it last time:

See http://lists.freedesktop.org/archives/hal/2005-October/003538.html
and quoting from http://live.gnome.org/GnomePowerManager/FAQ :
----
GNOME Power Manager doesn't spin down my hard-drive!

After numerous debates, the consensus was that is was not a good idea to
add this functionality to HAL. It's was decided user-configurable
powermanagement was not really required when modern hard disks have
really intelligent powermanagment.

A disk on Low Power idle need less than 1 Watt per hour. For a normal
battery with 50000mWh you could run the harddisk for over 50 hours. If
you do not read/write from/to the harddisk the disk regulates power, but
never shuts down the device. The reason is easy: you lost more power
with each startup than to leave the harddisk online somewhere between
'Active idle' and 'Low power idle' (depends on the model/manufacturer).
The other reason to leave this to the internal powermanagement of the
disk is: the time needed to reactivate the device. You lose more
performance than you lose power between 'Active idle' and 'Low power
idle'. If you use a journaling file system you normally need to flush
periodically. This could run in a race between shut down device and
restart device by system to flush. This means more power consumption as
you change nothing. You can't set powermanagement for exteral USB
harddisks, because you can't send the needed commands over the USB link
to the disk.
----

So maybe this is not worth the trouble?

CU
thl

@Richard: the link to the FAQ in the top header on
http://www.gnome.org/projects/gnome-power-manager/
gives a 404; the one in the right "Feedback" section point to a URL that
redirects the user to
http://svn.gnome.org/viewcvs/*checkout*/gnome-power-manager/trunk/docs/faq.html
which doesn't work.