Mark Thomas wrote:
> To Bart Samwel:
> 
> If the laptop is idling, with no apps doing anything that requires the
> disk, then I expect the disk to park, then spin down and stay spun down.
> You are correct that dirty pages will get flushed out within 30s, but
> the point is that if the user is not doing anything (or is doing
> something irrelevant to the hard disk like watching a DVD, or reading a
> cached [clean] document) then there should be no dirty pages to be
> flushed.  These are both of the use cases in
> https://blueprints.launchpad.net/ubuntu/+spec/power-management-in-ubuntu
> 
> This works in linux now as long as you don't have things being written -
> you can try it out by rebooting to single user mode so no processes
> other than sh are running.  ACPID on certain laptops was an extreme
> example, as it was logging at a particularly high rate, but there are
> other daemons and applications that needlessly read from or write to the
> hard disk.  Thunderbird, for example, should be using inotify, not
> polling the mail file (I assume that's what it's doing).

Unfortunately, there are many cases where the accesses are desired, 
unavoidable behaviour. For instance, I have Thunderbird set to retrieve 
mail from imap as it arrives. I get a new e-mail about every minute. So 
here's at least one user for which this will never work. If, at some 
point, Ubuntu will assume that no apps access the disk unnecessarily 
(because they changed them to work like that), and then enables power 
management to the drive using that assumption, it will start destroying 
my hard drive yet again because of the way I use the laptop. Avoiding 
disk I/O in the default install, while a noble thing to do, can _never_ 
be used to justify enabling aggressive power management on drives by 
default.

> We should find these daemons and applications (at least the ones in the
> standard ubuntu install) and fix them so they don't access the disk
> unnecessarily.  Starter for ten: ACPID.

I vote for enabling noatime first. :-)

-- 
Hard drive spindown should be configurable
https://bugs.launchpad.net/bugs/17216
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