Modius Data Center Blog

In 2007, the “Energy Independence and Security Act” was passed by congress and is sometimes referred to as “HR6” (see below). In this energy efficiency Act, Section 453 is a section dedicated to the application of this Act to the datacenter and the timeframes specified for doing so.

In general, the Act identifies a national goal by the year 2011 for all corporations to fully understand their energy consumption with some level of granularity. Now what is important here is that the Act appears to have raised some significant awareness across all ranks and corporate executives (“CxO”) that energy consumption is not only the largest (and rapidly growing) component of IT spending, but the details of this usage almost entirely an unknown. Assuming the likely scenario that the relevant government agencies continue to push for energy efficiency and independence, the HR6 Act will be applied to ALL companies within the US, public or private, and will become a hot topical discussion item in all of the coming stake-holder and shareholder meetings alike. This will affect us all in 2011!

As a background, the Act considers any facility or portion of a facility that “primarily contains electronic equipment used to process, store, and transmit digital information” and which “uses environmental control equipment to maintain the proper conditions” to be a datacenter, dedicated or not. So, essentially any company with IT of any nature will be well advised to consider “HR6-453” very strategically and make plans towards its goals now.

The good news is that the Act as written today, is focused on “Eco-Reporting” of all IT and facility assets alone, rather than the control and active reductions of energy consumption to any prescriptive level. (Those recommendations and opportunities will come next). It articulates that baselines should be drawn up that reflect “datacenter efficiency holistically, reflecting the total energy consumption” for IT equipment and the facilities around which they are housed. It recommends that these baselines be documented, auditable and available for analysis or governmental submission (if requested) over the next year.

Towards this end, monitoring systems should be evaluated with specific projects identified and put in place THIS YEAR (2010) that have the ability to measure and view energy consumption for all IT related consumption, equipment, cooling, facilities, etc. These systems will have a unique opportunity today to be initially deployed for compliance with HR6 in 2011, and yet at the same time become the framework and basis for the next expected phase of (likely) mandated behavior which will deal with actually increasing the efficiency for the IT function across all companies in the US.

Additionally and in support of this and subsequent Acts, the EPA is busy developing metrics in their Energy-Star programs which will set efficiency KPIs associated with IT equipment. In short order, guidelines (and later mandates) will exist that require the active monitoring and reporting, usage of increasingly efficient equipment, cooling and facilities infrastructure equipment, and the continuous optimization of the entire IT ‘system’ for increased energy efficiency much like ITIL has been suggesting for years. Given the roadmap ahead, now is the time to start planning for the inevitable.

Mark Harris
Vice President, Product Management
Mark.Harris[at]Modius.com

One of the key power usage metrics that I often find our customers requesting is  Available Redundant Capacity (ARC). This metric can mean different things to different people, but in simple terms, we at Modius like to define it as the amount of IT load that can be added to a data center system as a whole without sacrificing redundancy.

When viewed from the rack, row, room, or building level (or even across a network of data centers at the enterprise level), ARC provides a simple way to answer the question: “Where can I safely add new IT equipment without overloading and potentially bringing down my facility?”

Typically, most data centers don’t calculate ARC. Instead, operators set a simple alarm threshold on the Actual Loadof each device. For example, if the power load reaches 50% on a device (or more often 40% when de-rating), then the device or the monitoring system will throw an alarm.

However, this simple approach to thresholding based on device power usage doesn’t effectively capture all the conditions of the broader power distribution system. There can be hidden capacity that allows for safe failover, even though simple device-level thresholding suggests otherwise.

The goal of system ARC is to identify where you can handle additional load without sacrificing system redundancy. To calculate ARC for power of a device in a dual-feed situation, the calculation is simply:

ARC = {Device Capacity}/2 – {Actual Load}

In most cases, the Device Capacity will be de-rated to allow for some margin. In the case of power capacity, it is common to de-rate apparent power (kVA) capacity by 80%. ARC can also be expressed in real power (kW) if you know or can estimate the power factor of the load. It is even more important to de-rate the capacity in the case kW measurements to allow for potential load problems that could degrade power factor.

Below is an ARC-based dashboard in action:

Here, the top panel shows how ARC has been calculated for 6 different data centers, along with a measure of cooling overhead. The lower panel shows the drill down for one of the sites.

When calculating the overall ARC for devices in parallel, you can add the ARCs of the individual units. For instance:

UPS A has 10 kVA ARC
UPS B has 8 kVA ARC
Together, they have 18 kVA ARC
Interestingly, it is possible to have a safely redundant system even though one of the individual devices has a negative ARC. For example:

UPS A has 3 kVA ARC
UPS B has −2 kVA ARC
The net ARC of the system is a small but safely positive 1 kVA
In this case, even though one UPS is nominally overloaded according to the simple one-device threshold, either UPS can fail without dropping any load.

Calculating system ARC from the individual device ARCs in this way assumes that the capacities of both parallel components are the same. This is most often the case, but in the rare instance that it is not, then you have to total the actual load across the devices, and compare it to the (de-rated) capacity of the smaller device. This ensures that the most-limited device can handle the entire load.

Some questions may arise when the load is imbalanced, as in the examples above. Such imbalances may arise because some of the load is not configured redundantly. Some loads also do not balance themselves between the two power paths. The ARC calculation doesn’t depend on knowing such details. Of course, any non-redundant load will be dropped if it loses its power source; however, as long as the system ARC is positive you know that any redundant load will be protected regardless of which power source is lost.

In summary, the goal of system ARC is to identify where you can handle additional load without sacrificing system redundancy. With parallel equipment, you can total the ARC of all components if they have the same capacity rating. When looking at ARC along the power chain, the correct system value will be the minimum ARC of any one set of components.

Kind regards,

Jay H. Hartley, PhD
Director of Professional Services
Jay.Hartley@Modius.com