Everyone's talking about how the 35 to 40 percent energy savings promised by so-called green data center initiatives can help MIS operations dramatically reduce both their operating expenses and their environmental impact. But despite the buzz, there is not much being said about the most efficient and cost-effective way to achieve these savings-or how to measure them. Meanwhile, the ambitious claims being made by many hardware and software vendors make it hard to understand how much their particular solution adds to your operation's overall energy efficiency.
Instead of focusing on the exotic technologies used by newly constructed, ultra-efficient data centers such as those used by Google, this article will deal primarily with the best ways to improve the efficiency of the many middle-aged and older facilities that still constitute the majority in use by enterprises, universities and government agencies. Since most real-world facilities have finite budgets and cannot afford downtime, we'll pay special attention to upgrades that offer fast payback periods and pose a minimum of disruption to normal operations.
Metrics, models and methodologies
One popular efficiency ratio that we'll use to understand the effectiveness of our upgrades is the Power Usage Effectiveness (PUE) factor, defined as the ratio between the power consumed by the data center facility itself and the power consumed by its IT equipment.
PUE = Total Facility Power/IT Equipment Power
Although PUE is a widely-accepted way to describe how data centers use their energy, care must be used when interpreting the results it produces. One must always keep in mind that PUE is most useful for tracking the effect of changes you make on the infrastructure side and less useful for tracking the improvements resulting from reducing the energy consumption of your data center's IT equipment. Because it is a non-scalar ratio, cutting your equipment power consumption can actually result in a higher PUE.
The data center we'll use in this example is a traditional "MIS center" that supports the computing and networking needs of a mid-sized, brick-and-mortar enterprise-perhaps an insurance company, manufacturer or biotech operation. Its 7,500-square-foot floor plan was carved out of an underused floor of the company's headquarters back in the late 1980s. This was a time when equipment was expensive, energy was cheap and the room still bears the white walls, white floors and bright lighting that were the standard decor of the era. The mainframes and mini-computers it once housed have given way to a patchwork of servers and disk farms that have been added over the years as demand dictated and space permitted.
Our model data center's power consumption has steadily grown with the addition of new equipment and now stands at around 1.5MW. Although the average PUE for all data centers is somewhere around 2.7, most of the "mature" facilities we're concerned with have PUEs that range from 3.0 to 5.0, so it's reasonable to assume that ours runs in the neighborhood of 4.0.