What will be the most appropriate measurement of efficiency in the data center of the future?

In the past we explored new metrics for evaluating data centers, such as data center density (cycles per square foot), automation (admin staff per unit of data-center density), and storage density (storage utilization per square foot). These measures attempted to quantify both the rapid growth and the continuing concentration of compute power and storage in the limited spaces of the enterprise data center, managed by limited numbers of data center staff. They focus the attention on strictly internal parameters: space, staffing, compute cycles, storage utilization.

Since then, energy prices have continued to rise steadily, and awareness of both the financial and the environmental costs of enterprise computing has changed the way we view large data centers.

As we retool IT to be better stewards of both enterprise and natural resources, greening our data centers, other measures should now come to the fore as well, based on data centers’ interfaces with the environment. The basic means of interaction are energy consumption and heat production. So, other metrics merit consideration:

* Computational power efficiency, measured in cycles per kilowatt-hour, comparing compute activity to the energy required to enable it. For a true reflection of energy input, data center managers will measure actual inputs of electricity consumed rather than make calculations based on component ratings, and will measure all inputs, including power going to HVAC and lighting. (Feel free to substitute the SI units if you like metric units better; 1 kWh = 3.6 megajoules.)

* Computational heat efficiency, measured in cycles per BTU of heat produced. This compares computation to its main waste product, heat. This in some ways overlaps the measurement of energy efficiency, since the energy required to cool the data center must be included in the energy draw of the data center. However, it is a useful direct measurement of computational impact on the environment, especially in colder climates, where cooling can for several months in a year be a matter of circulating outside air rather than chilling hot inside air. The fact that cooling is achieved mainly by dumping heat directly out of the data center doesn’t obviate the fact that the heat is being produced. (Yes, you can also measure this in joules, 1 BTU = 1055 J, but remember that this is joules out, not joules in.)