Google is biased, but it has put together a strong argument for saving money and energy in the cloud, says Peter Judge
If you have been wondering whether your email would use more energy in-house or in the cloud, Google would like you to relax. It’s done some sums, and given the cloud a green bill of health.
Now, this is no surprise. Google wants your apps in its cloud, and has always lined up strong arguments in its favour. When users worry about cloud security, Google argues that cloud apps are actually more secure.
When people fret that cloud is less reliable, for instance when Google’s servers, or Microsoft’s, have a bad day, Google can argue that internal IT departments also fall over from time to time – although there is less concrete evidence on that subject.
And when activists like Greenpeace raise concerns about the growth of data centres used for cloud services, Google’s response is that overall, the cloud is green, because it replaces less efficient data centres, or isolated servers, on the customers’ own premises.
Spelling it out in detail
The argument is fairly easily made, and Google has set it out well in a short white paper which concludes that using the cloud can be 80 times more efficient than running your own servers, because servers used by cloud companies will be used more efficient and run at a lower power usage effectiveness (PUE).
First, Google compares the servers used in small, medium and large companies.
Small companies with 50 users will tend to have small multi-core servers with local storage, which could support about 300 users, and draw 200W.
A medium size company with 500 users, will have a larger server, that can support up to 1000 users, and draws about 450W.
Large companies with 10,000 users, will have ten servers similar to the medium size company.
So the small company starts out using more Watts per user, but it gets worse when the companies provide back-up servers. Small companies need a whole spare server (N+1) , doubling the energy used, while the large company just needs two spare servers in its pool of ten (N+0.2),
That leaves the small, medium and large companies using 8W, 1.8W, and 0.54W per user respectively.
Factoring in the cooling costs
The companrison gets worse when Google factors in the other costs involved in running the servers – specifically cooling them down. Outside of highly efficient data centres, it usually takes more energy to cool a server down than it does to drive it, leading to a PUE greater than 2.
This applies equally to servers which are in network closets, says Google. They don’t have separate cooling systems, but they apply a load on the office cooling system – and since the office system is designed to keep the whole space at a liveable temperature, Google says it will be less efficient, so the small business has a PUE of 2.5, while the large company gets down to 1.6.
So the actual energy use per user for small medium and large companies, is 20W, 3.2W and 0.9W.
Having gone through all that, Google then reveals its own figures, claiming it uses less than 0.22W per user, and has a PUE of 1.16, and a total power per user of less than 0.25W – less than a third of the efficient big company and about one-eightieth of the power used per user by the small company.
Multiplying that across a whole year, Google reckons Gmail can save big companies 7.6kWh of energy per user, and 175kWh for small companies.
Google has a bias here, but the calculations are sensible. The only factors missing are the increased networking usage (which is negligible) and the tendency for cloud to encourage greater and more continuous use of mobile devices (which is a general trend and not down to Google).
It should also be said that these are not huge savings – the cost would be about £1 per user for the small company and £15 per user for the big company (depending where they buy their electricity).
But they are savings worth making – in money and emissions – and Google points out that it offsets all its cloud energy, so it is carbon neutral.