• Faceplate Values. Each manufacturer places a service value ‘plate’ which identifies things like model and serial numbers, manufacturer’s contact information, safety certifications and power requirements. The power requirements are usually listed as the voltage range acceptable for the included power supplies, as well as the maximum current to be drawn by any configuration and working condition of the device. For a complex device, this faceplate power consumption value is listed as the maximum possible and may be 4 or 5 times the actual power being drawn in normal operating conditions. Since this is printed information required on every device, it essentially has no additive administrative no-cost.
• iPDU Monitoring per outlet. Newer environments have begun to deploy measured or metered power distribution devices within each rack. These iPDU have enough intelligence to allow network inquiries to be made of the iPDU itself, with the most granular of these devices offering discrete values for the power being consumed PER-OUTLET. These PER-OUTLET iPDUs make ideal sources of raw power consumption values, although they tend to be costly to do so.
• Monitoring via operating system service. Most modern hardware telco, server and switch designs and their associated operating systems include what is known as ‘System Services’ or ‘Daemons’ which are intended to allow access to granular operating information. In most modern cases, device drivers are included in the standard software builds which enable power consumption metrics to be read from the actual power supply unit, assuming that the power supply was instrumented in hardware when the device was manufactured. In cases where this hardware instrumentation exists, there are no additive costs to gaining access to the power consumption for these devices across an IT infrastructure.
• Modeling the device. It could be argued that a tremendous portion of the installed IT equipment that was purchased more than 3 years ago has little or no instrumentation capability in hardware. In these cases it is impossible to programmatically read power consumption metrics. Instead one approach has been to model the power consumed based upon a model of the hardware configuration of the device. Mostly for servers, it could be argued that a good approximation for a device can be calculated by knowing an inventory of components inside each device, and then the power consumption of each of those components. Coupled with some workload information and a fair assessment of consumption can be derived.

It should be noted that each and every Enterprise will likely find themselves dealing with MULTIPLE approaches (from the above list) in determining power consumption. Some devices and configurations will lend themselves to highly granular network inquiry, while other older devices may need to be modeled to determine power. It is these sources of power consumption that will need to be gathered, normalized and then ultimately fed into some form of higher value asset or resource management suite.