PUE, Are you Managing Power, Energy or Productivity?

October 14, 2009 – 11:28 pm

With a renewed focus on Green IT including energy Efficiency and Optimization of servers, storage, networks and facilities, is your focus on managing power, energy, or, productivity?

For example, do you use or are interested in metrics such as Greengrid PUE or 80 Plus efficient power supplies along with initiatives such as EPA Energy Star for servers and emerging Energy Star for Data Center for Storage in terms of energy usage?

Or are you interested in productivity such as amount of work or activity that can be done in a given amount of time,or how much information can be stored in a given footprint (power, cooling, floor space, budget, management)?

For many organizations, there tends to be a focus and in both managing power along with managing productivity. The two are or should interrelated, however there are some disconnects with some emphasis and metrics. For example, the Green grid PUE is a macro facilities centric metric that does not show the productivity, quality or measure of services being delivered by a data center or information factory. Instead, PUE provides a gauge of how the habitat, that is the building and power distribution along with cooling are efficient with respect to the total energy consumption of IT equipment.

As a refresher, PUE is a macro metric that is essentially a ratio of how much total power or energy goes into a facility vs. the amount of energy used by IT equipment. For example, if 12Kw (smaller room/site) or 12Mw (larger site) are required to power an IT data center or computer room for that matter, and of that energy load, 6kWh or 6Mw, the PUE would be 2. A PUE of 2 is an indicator that 50% of energy going to power a facility or computer room goes towards IT equipment (servers, storage, networks, telecom and related equipment) with the balance going towards running the facility or environment which typically has had the highest percentage being HVAC/cooling.

In the case of EPA Energy Star for Data Centers which initially is focused on the habitat or facility efficiency, the answer is measuring and managing energy use and facility efficiency as opposed to productivity or useful work. The metric for EPA Energy Star for Data Center initially will be Energy Usage Effectiveness (EUE) that will be used to calculate a ratting for a data center facility. Those data centers in the top25 percentile will qualify for Energy Star certification.

Note the word energy and not power which means that the data center macro metric based on Green grid PUE rating looks at all source of energy used by a data center and not just electrical power. What this means is that a macro and holistic facilities energy consumption could be a combination of electrical power, diesel, propane or natural gas or other fuel sources to generate or create power for IT equipment, HVAC/Cooling and other needs. By using a metric that factor in all energy sources, a facility that uses solar, radiant, heat pumps, economizers or other techniques to reduce demands on energy will make a better rating.

By using a macro metric such as EUE or PUE (ratio = Total_Power_Used / IT_Power_Needs), a starting point is available to decide and compare efficiency and cost to power or energize a facility or room also known as a habitat for technology.

Managing Productivity of Information Factories (E.g. Data Centers)
What EUE and PUE do not reflect or indicate is how much data is processed, moved and stored by servers, storage and networks within a facility. On the other hand or extreme from macro metrics are micro or component metrics that gauge energy usage on an individual device basis. Some of these micro metrics may have activity or productivity indicator measurements associated with them, some don’t. Where these leave a big gap and opportunity is to fill the span between the macro and micro.

This is where work is being done by various industry groups including SNIA GSI, SPC and SPEC among others along with EPA Energy Star among others to move beyond macro PUE indicators to more granular effectiveness and efficiency metrics that reflect productivity. Ultimately productivity is important to gauge,  the return on investment and business value of how much data can be processed by servers, moved via networks or stored on storage devices in a given energy footprint or cost.

In Figure 1 are shown four basic approaches (in addition to doing nothing) to energy efficiency. One approach is to avoid energy usage, similar to following a rationing model, but this approach will affect the amount of work that can be accomplished. Another approach is to do more work using the same amount of energy, boosting energy efficiency, or do same amount of work (or storage data) however with less energy.

Tiered Storage
Figure 1 the Many Faces of Energy Efficiency Source: The Green and Virtual Data Center(CRC)

The energy efficiency gap is the difference between the amount of work accomplished or information stored in a given footprint and the energy consumed. In other words, the bigger the energy efficiency gap, the better, as seen in the fourth scenario, doing more work or storing more information in a smaller footprint using less energy. Clock here to read more about Shifting from energy avoidance to energy efficiency.

Watch for new metrics looking at productivity and activity for servers, storage and networks ranging from MHz or GHz per watt, transactions or IOPS per watt, bandwidth, frames or packets processed per watt or capacity stored per watt in a given footprint. One of the confusing metrics is Gbytes or Tbytes per watt in that it can mean storage capacity or bandwidth, thus, understand the context of the metric. Likewise watch for metrics that reflect energy usage for active along with in-active including idle or dormant storage common with archives, backup or fixed content data.

What this all means is that work continues on developing usable and relevant metrics and measurement not only for macro energy usage, also, to gauge the effectiveness of delivering IT services. The business value proposition of driving efficiency and optimization including increased productivity along with storing more information in a given footprint is to support density and business sustainability.


Additional resources and where to learn in addition to those mentioned above include:

EPA Energy Star for Data Center Storage

Storage Efficiency and Optimization – The Other Green

Performance = Availability StorageIOblog featured ITKE guest blog

SPC and Storage Benchmarking Games

Shifting from energy avoidance to energy efficiency

Green IT Confusion Continues, Opportunities Missed!

Green Power and Cooling Tools and Calculators

Determining Computer or Server Energy Use

Examples of Green Metrics

Green IT, Power, Energy and Related Tools or Calculators

Chapter 10 (Performance and Capacity Planning)
Resilient Storage Networks (Elsevier)

Chapter 5 (Measurement, Metrics and Management of IT Resources)
The Green and Virtual Data Center (CRC)

Ok, nuff said.

Cheers gs

Greg Schulz – Author Cloud and Virtual Data Storage Networking (CRC Press), The Green and Virtual Data Center (CRC Press) and Resilient Storage Networks (Elsevier)
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