[mythtv-users] Trimslice ARM PC

[Michael T. Dean]

On 12/27/2011 05:17 PM, Gary Dawes wrote:
> Getting back on topic though, I mentioned on here last year that I had 
> installed debian and Mythtv on a Pogoplug to run as my Master backend.
>
> I was advised by several people on here that it was not a good idea 
> due to the processing required by the rescheduler processes, and that 
> they would take a lot longer.
>
> I changed tack, and my Myth Master is still the power hungry dual-core 
> AMD, but it now shuts down when not required,

This is, by far, the best way to save power.  Whether you run a 25W Atom 
system or a 25W Core i3/i5 system or an 80W Core i system you built 
before you were thinking about power usage, turning the system off for 
18hrs a day and running it for only the 6hrs a day it's actually being 
used (just a wild guess estimate--that's actually far more conservative 
than my usage of maybe 4hrs per day) will save a lot of power.  (And 
note that even if you have a 400W power supply, you're likely pulling 
closer to the 80W range or so unless you chose parts that are as 
inefficient as possible--i.e. you made a gaming system by buying the 
top-end/pushing-the-envelope-of-the-current-technology-generation parts 
instead.)

> and the Pogoplug acts as a "wake-on-lan concierge". When Myth shuts 
> down it writes the wakeup time to the pogoplug, which then executes 
> WakeonLan at the desired time.
>
> This was all due to the motherboard  not doing wakeup correctly on 
> it's own.Works well for me, and it has reduced my bills significantly.

Yep...  Going with the above numbers:

80W system:
     Run for 24hrs/day = 1920Wh/day = 57.6kWh/mo = $6.91/mo @ $0.12/kWh 
=~ $82.92/yr
     Run for 6hrs/day = 480Wh/day = 14.4kWh/mo = $1.73/mo @ $0.12/kWh =~ 
$20.76/yr
Savings for shutting down 18hrs/day: $5.18/mo = $62.16/yr


25W system:
     Run for 24hrs/day = 600Wh/day = 18kWh/mo = $2.16/mo @ $0.12/kWh =~ 
$25.92/yr
     Run for 6hrs/day = 150Wh/day = 4.5kWh/mo = $0.54/mo @ $0.12/kWh =~ 
$6.48/yr
Saving for shutting down 18hrs/day: $1.62/mo = $19.44/yr

Or, more simply, if you shut down the system for 3/4 of the day, you 
spend only 1/4 as much on electricity for the system.  :)

And, if you have an 80W system, and you shut it down for 3/4 of the day 
and run it only for the 1/4 of the day when you're recording and/or 
watching TV, you're now spending $1.73/mo to run the MythTV box instead 
of $6.91/mo ($5.18/mo savings).

Now, you decide to replace that 80W system with a 25W Atom system (or 
Core i system or whatever--the point being you're replacing the 80W 
system with a system that uses less power).  To run that 25W system for 
6hrs/day costs you $0.54/mo.  That means, switching to a 25W system is 
now saving you only an additional $1.19/mo.

In other words, once you cut the power usage to 1/4 by turning off the 
system when not it use (3/4 of the time), you've only got 1/4 left to 
save.  Whereas shutting down the 80W system when not in use got us a 
nice savings of $5.18/mo, the most savings we could possibly get from 
any other change at this point is $1.73/mo--as we've already cut out 3/4 
of the power usage.

If you go with a 2-6W Trimslice instead of a 25W Atom/Core i system, it 
would save you some amount of money versus running a 25W Atom/Core i 
system, but couldn't possibly save you more than $1.62/mo--the amount 
you spend running a 25W system for the 6hrs/day it's in use.  If you 
think that the $19.44/yr is a good target for savings, more power to you 
(or should I say, "less power to you"?), but realize that at some point, 
you're going to be cutting into functionality/responsiveness/usefulness 
of the system, so make sure you compare that cost to the benefit (saving 
somewhere less than $20/yr).  (Not to mention the cost of trying to make 
MythTV work on that system.)

So, regardless of what system you have and how much power it uses, if 
you shut it off when it's not in use, you're likely to get a good amount 
of savings just from choosing to not waste power by running it when not 
necessary.  And, beyond a certain point, you have to consider the law of 
diminishing returns.

Mike

* Yearly numbers are approximate because I'm using 12 months of 30 days 
each, so we're not accounting for 5 days/yr.