McElroy then proverbially dropped the other shoe: “Despite the growth in rack PDUs with higher power ratings, IHS finds that average rack power densities are not as high as the rack PDU power rating data might suggest. IHS estimates that average rack power density globally is approaching but remains below 5 kW per rack.”
She detailed the following factors that have caused power density per rack to rise more slowly than they were expected to 5 to 10 years ago.
Advances in the energy efficiency of power supplies and IT equipment has increased the achievable compute per watt.
The emergence of low-power servers such as Atom processor-based units designed to have low power draw are increasingly used for less-power-intensive tasks like data storage.
Server virtualization allows users to run servers at higher capacity, for example 80 percent instead of 20 percent capacity. Instead of adding additional servers, users are now running current servers closer to full capacity, which generally results in less power draw than adding new servers to perform the same amount of computing.
McElroy also drew attention to environments in which data center rack densities have risen: “While average rack densities still remain below 5 kW worldwide, densities of up to almost 50 kW have been implemented in applications such as supercomputing. It’s no longer uncommon to see rack densities of 20 to 30 kW in some applications. Average rack power densities will continue to rise in the next five years as a result of the increased number of servers that can fit in one rack as well as increases in rack heights. However, it will likely take a few years for actual rack power densities to catch up with power ratings on rack PDUs that end users are purchasing.”