In this article i answer the following question: When does the energy cost of running the FreedomBox software on a desktop computer justify buying specialized low power hardware? The answer to this question may surprise you.
Not long ago a reader of my blog asked me why he could not use his desktop computer to run the FreedomBox software. I answered that he could, but it would not be very economical. I gave him the following example: My desktop computer at the time consumed 93 Watt when idle. Keeping this machine running for a year would cost me 186 EUR. The energy costs of my 11 Watt NAS “FreedomBox edition” is just 22 EUR a year. In this example it is clear that it pays to buy special hardware for the FreedomBox. For my new energy efficient desktop computer (23 Watt idle) the situation is different.
In a previous article (Free hardware for the FreedomBox software) i argued that the cheapest hardware for the FreedomBox is hardware that you need anyway. If you can run the FreedomBox software on this hardware without changing it’s function, then the hardware for the FreedomBox costs you nothing. This is true for always-on devices like wireless routers and NAS servers. With these devices the only cost of running the FreedomBox software is the cost of the extra energy which is probably very low. For desktop computers the situation is different. Desktop computers consume more energy than specialized always-on devices and are only used part of a day (normally).
How much does it cost to use a desktop computer to run the FreedomBox software?
Calculating the costs is very easy. Because you need the desktop computer anyway, the price does not enter the equation. Only the extra energy costs are important. This leads to the following equation:
Cd = Pdi * Td * Ckwh/1000
where:
Cd : Cost of running FB software on a desktop computer Pdi : Power consumption in Watt of the desktop computer when idle Td : Time in hours the desktop computer is running FB software exclusively Ckwh : Kilowatt-hour price.
Because the FreedomBox software is mostly sleeping, i only take the idle power consumption into account.
How much does running a dedicated FreedomBox device cost?
With a dedicated device you have to enter the price of the device into the equation:
Cf = Cfd + Pfi * Tf * Ckwh/1000
where:
Cf : Cost of running FB software on a dedicated FB device Cfd : Price of the FB device Pfi : Power consumption in Watt of the dedicated FB device when idle Tf : Time in hours the FB device is running
Some quick calculations
Let’s compare the cost of my (very) energy efficient desktop computer with a DreamPlug. I use the following parameters:
Pdi = 23 W
Td - do not correct the time for non FB use of the desktop computer.
Cfd = 163 EUR DreamPlug + 50 EUR USB hard-disk = 213 EUR
- assume a 3 year life of the DreamPlug
Pfi = 5 W DreamPlug + 5 W USB hard-disk
Ckwh = 0.25 EUR
For a 3 year period this calculates to:
Cd = 23W * 3*365*24 * 0.25/1000 = 151 EUR Cf = 213 EUR + 10W * 3*365*24 * 0.25/1000 = 278 EUR
In this example using a DreamPlug as a dedicated FreedomBox device is not economical. Even with no correction for the time the desktop computer is used for it’s normal tasks, the DreamPlug solution is almost 2 times as expensive.
Using the DreamPlug results for a 3 year period you can calculate the idle power consumption of a desktop computer that is just as expensive as a dedicated DreamPlug. This turns out to be 42 Watt.
Let’s calculate the costs of running a Raspberry Pi model B for three years.
Cfd = 39 EUR (32.70 GBP * 1.2 EUR/GBP) + 50 EUR USB HD = 89 EUR Pfi = 1 W Raspberry Pi + 5 W USB HD = 6 W Cf = 89 + 6W * 3*365*24 * 0.25/1000 = 128 EUR
The very low power Raspberry Pi is the winner. It would save me 33 EUR over a period of three years. For me, this is not a good reason to buy a Raspberry Pi. (Still think i buy one, just for fun!)
(Note: in these calculations i have not corrected for the time i use my desktop computer for it’s normal tasks. If i correct for the 8 hours a day i use my system for desktop-tasks, the desktop costs for running the FreedomBox software would be 100 EUR.)
Conclusion:
If you have desktop computer with low idle power consumption, then there is no (economical) need to buy special low-power hardware for running the FreedomBox software.
6 comments
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Wookey
April 1, 2012 at 01:11 (UTC 2) Link to this comment
What you are saying is that if you already have a fairly low-power computer it’s not worth buying an even lower-power computer for always-on use unless that computer is very low-power or very cheap.
But of course if you just bought a suitable ARM box then you wouldn’t need to buy the low-power server. And your ower-all consumpotion would be a lot lower. Yes, of course once you have one computer that is low-power you don;t really need a second one – but presuming that the first one must be an x86 desktop seems to me to be a false premise.
Secondy you over-estimate the power-consumption of low-power machines in idle. A Pi will be max 3W, min should be less than 1W (quite highg due to simple PSU). Better devices will idle at a maybe 200mW. Put htose number in and suddenly it is worth doing over 3 years.
Ultimately any low-power computer is good. Your desktop is very good for a desktop, but almost any arm-based device will be a lot better. Even my x86 x200 thinkpad is better. (9W idling, nearly all screen). For always-on devices I’d never consider anything that used more than 10W these days, and aim a _lot_ lower, which is actually mostly about disk power management in practice, I’ve found over last couple of years.
robvanderhoeven
April 1, 2012 at 19:12 (UTC 2) Link to this comment
What i’m saying is: People will always need some kind of general purpose computers. These computers (generally Intel/AMD powered) can also be used for the FreedomBox if they have a modest idle power consumption. Anything with an idle power consumption below 40 W will probably be cheaper than buying a dedicated DreamPlug for the FreedomBox software. My estimation is that any Intel/AMD computer with integrated graphics on the CPU and no dedicated GPU will have an idle power consumption below 50W.
I’m not against ARM, quite the opposite. I like ARM hardware and have several ARM powered devices (like everyone these days, but i’m aware there is an ARM SOC inside
. What worries me is that many people falsely think you need special hardware for the FreedomBox. For me the FreedomBox is a software project. Just like the Debian community i welcome any hardware that runs the software. To give people the impression that they need special hardware (when they don’t) is bad for the FreedomBox.
Thanks for the info about the Raspberry Pi power consumption. I will update my article.
Anders
April 1, 2012 at 18:25 (UTC 2) Link to this comment
Some small errors:
Cd = Pdi * Td * Pkwh/1000 where Pkwh should be Ckwh
In the investment you have forgot to calculate on the cost for FB desktop sollution. You still need that dedicated disc space to FB. As a dedicated disc or increased disc capacity when you buy the desktop computer.
What is interesting is two things. Investment and running costs.
Investment is a “one shot” cost and running cost is during your device life time.
Investment in euro and running cost in Wh/year should be what we looking for.
And if you run your FB software on your desktop there are some increased risk of getting your FB hacked. As you use your computer to surf, which increases the risk.
So I don’t think that there are that large economical difference, and there are some other reasons to not run FB on your desktop computer.
Even there are some good arguments to use modern desktop hardware to run a dedicated FB.
Information to base which sollution to use is always good.
robvanderhoeven
April 1, 2012 at 19:43 (UTC 2) Link to this comment
You are probably right about the running costs, but i wanted to give some quick examples that most people can undestand. Just to show that Intel/AMD desktop computers can be used economically for the FreedomBox software. I hope to get a more balanced hardware discussion.
I think running the FreedomBox software on desktop computers can be done perfectly safe. You only have to run the FreedomBox software inside a virtual machine. A virtual machine is an excellent way to distribute the FreedomBox software too.
One benefit of running the FreedomBox software on desktop hardware is the far superior performance of desktop hardware. To give you an example. My website currently runs on ARM hardware. This hardware generates my WordPress homepage in 2.5 seconds. This is acceptable, but not great. Some time ago i started working on a python-powered version of my website. This version can serve 25 pages/sec. To test the speed of my new desktop PC i benchmarked the same code and got a result of 800 pages/sec. The desktop hardware has over 30 times the performance when compared to the ARM hardware!
Norbert
June 3, 2012 at 22:08 (UTC 2) Link to this comment
You also assume that personal computers would be on all the time. For laptop devices this isn’t the case and dedicated hardware is the only way to provide 24×7 access.
robvanderhoeven
June 4, 2012 at 22:33 (UTC 2) Link to this comment
I know people that are using a laptop for downloading torrents 24/7. An old laptop can be an excellent FreedomBox server! BTW, you don’t have to dedicate a normal desktop/laptop to FreedomBox tasks only. If you run the FreedomBox software inside a virtual machine it will be isolated from the normal laptop/desktop functions (a virtual machine FreedomBox need about 512 Mb memory max, and not much processor power)