I’m not sure how many times I’ve read or been told that power is the number one cost in a modern mega-data center, but it has been a frequent refrain. And, like many stories that get told and retold, there is an element of truth to the it. Power is absolutely the fastest growing operational costs of a high-scale service. Except for server hardware costs, power and costs functionally related to power usually do dominate.

However, it turns out that power alone itself isn’t anywhere close to the most significant a cost. Let’s look at this more deeply. If you amortize power distribution and cooling systems infrastructure over 15 years and amortize server costs over 3 years, you can get a fair comparative picture of how server costs compare to infrastructure (power distribution and cooling). But how to compare the capital costs of server, and power and cooling infrastructure with that monthly bill for power?

The approach I took is to convert everything into a monthly charge. Amortize the power distribution and cooling infrastructure over 15 years and use a 5% per annum cost of money and compute the monthly payments. Then take the server costs and amortize them over a three year life and compute the monthly payment again using a 5% cost of money. Then compute the overall power consumption of the facility per month and compare the costs.

Update: fixed error in spread sheet comments.

What can we learn from this model? First, we see that power costs not only don’t dominate, but are behind the cost of servers and the aggregated infrastructure costs. Server hardware costs are actually the largest. However, if we look more deeply, we see that the infrastructure is almost completely functionally dependent on power. From Belady and Manos’ article Intense Computing or In Tents Computing, we know that 82% of the overall infrastructure cost is power distribution and cooling. The power distribution costs are functionally related to power, in that you can’t consume power if you can’t get it to the servers. Similarly, the cooling costs are clearly 100% related to the power dissipated in the data center, so cooling costs are also functionally related to power as well.

We define the fully burdened cost of power to be sum of the cost of the power consumed and the cost of both the cooling and power distribution infrastructure. This number is still somewhat less than the cost of servers in this model but, with cheaper servers or more expensive power assumptions, it actually would dominate. And it’s easy to pay more for power although, very large datacenters are often located to pay less (e.g. Microsoft Columbia or Google Dalles facilities).

Since power and infrastructure costs continue to rise while the cost of servers measured in work done per $ continues to fall, it actually is correct to say that the fully burdened cost of power does, or soon will, dominate all other data center costs.

For those of you interested in playing with different assumptions, the spreadsheet is here: OverallDataCenterCostAmortization.xlsx (14.4 KB).

–jrh