Whoa, please don't go all-conservative and throw away the baby with the
bathwater! I think the LM_BATT timeout should be set to a value that
achieves the best balance between the following goals:
#1: Power savings
#2: Not be irritating to users
#3: Not kill hard drives
Starting with #1: 15 minutes spindown timeout will achieve exactly _no_ power
savings, since it is enough to leave the drive always-on. The only way anyone
will achieve power savings with this setting is by leaving the laptop on but
not using it, otherwise the hard drive will _never_ spin down. But in that
situation, any sensible user will use a much better power saving option:
suspending. So you might as well remove laptop mode if you set it this high.
To achieve power savings, if Epiphany spins up the disk every 5 minutes,
you'll want the timeout to be set well _below_ 5 minutes, so that the
hard drive spends the better part of the 5 minutes spun down. First of
all, even spinning up every 30 seconds already gives almost the maximum
power savings, see the graph in this article:
http://www.linuxjournal.com/article/7539
I think any setting between 20 seconds and ~2 minutes can achieve
reasonable power savings (from max. 8 to max. 9.75 minutes spun-down
time, given 10 minutes MAX_LOST_WORK_SECONDS).
Regarding #2: It depends on the user's usage pattern, 5 seconds is too
low, but anything between 1 and 2 minutes is fine as long as users
realize that it gets them a lot of extra battery life.
Regarding #3: A typical laptop hard drive is rated for about 300,000
spinups. Taking a conservative laptop lifetime of 10 years, that's
30,000 spinups per year. Using it for 365 days per year leaves 82
spinups per day. A typical 8 hours of usage each day then gives us 10
spinups per hour to play with safely. That seems a bit low, but now
consider that, of these 8 hours, typically a maximum of 4 hours are
spent in battery mode (as a new battery charge is needed after that).
That increases this number to 20 spinups per hour.
Note that these numbers are pretty conservative. First of all, nobody
uses their laptops in battery mode for 4 hours _every single day of the
year_. Also, Consider that 4 hours spent in battery mode daily means a
full battery charging cycle every day, i.e., a useless battery after one
year. If the laptop is going to support this usage pattern, it will
require one replacement battery every year. It is pretty safe to say
that _nobody_ will ever buy 9 replacement batteries for a single laptop.
After 5 years, the laptop is obsolete, it will not get a new battery but
it will be retired and fulfill a role as granny's next laptop, spending
its last couple of years plugged in, with the hard drive spun up.
Therefore, the number of spinups per hour can probably be safely
increased to 40, even. That's one spinup every 1.5 minutes _on average_.
With some cycles shorter and some cycles longer, a 60-second timeout
seems defensible. That'll yield some spinup intervals of 5-10 minutes,
and some of 61 seconds. It'll definitely even out.
--
Laptop HDD powerdown every 5 seconds
https://launchpad.net/bugs/29529
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