Comment 27 for bug 952556

On Tue, Mar 20, 2012 at 06:15:57PM -0000, Swâmi Petaramesh wrote:
> On my Dell XPS M1330, it's enough to specify "apm_battery = 128" in
> /etc/hdparm.conf to solve the issue. That's the "old" value...

> So I confirm that this parameter was the cause of the issue on 2
> machines, and the fix fixes it on both.

However, that's not a proper fix because apm_battery = 128 is not guaranteed
to spin the disk down when idle; 127 is the first value that enforces
spin-down.

We can set a default spindown_time value to make sure we're not spinning
down unless the disk is idle for, say, 2 minutes, but I'm not positive this
actually corresponds to Load_Cycle_Count anyway which is supposed to be
about head parking rather than actual disk powerdown. Could you test
whether you see a difference in the load count if you keep apm_battery at
127 but set spindown_time to 24 in /etc/hdparm.conf?

Ultimately, the reason that apm_battery is set to 127 is because when on
battery, we want to spin down the disk for power savings. But the only
effect the above changes will have is to prevent the disk spinning down at
all, and that's because something is hammering your disk and preventing it
from staying asleep. You may want to use the fatrace tool to examine the
causes of this, because those are the bugs that *really* should be fixed.