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Power availability is one of the most important challenges facing datacenters today. In the past, datacenter floor space has always loomed as the primary issue. Now, more and more datacenters run out of power availability before they run out of floor space. In addition, cooling requirements for dense servers are driving power demand and taxing the normal datacenter operational procedures.
Operations are not properly “tuned” to accommodate the new energy-hungry environment. This paper illustrates existing electrical consumption patterns and suggests various strategies for reducing consumption. Energy improvements can be made from both an equipment-planning perspective and an operational-practices perspective for both IT and physical infrastructure (power, cooling, rack, security, fire suppression, and monitoring) devices.
Energy Costs and Consumption
For years, electrical power usage was not considered a key design criteria for datacenters. Nor was electrical consumption effectively managed as an expense. In fact, many datacenter managers are unaware of what their monthly energy bill is. This is true despite the fact that the electrical energy costs over the life of a datacenter may exceed the costs of the electrical power system including the uninterruptible power supplies (UPS), or even exceed the cost of the IT equipment itself.
The reasons for this situation are as follows:
- Electrical bills are sent out long after charges are incurred. No clear link exists between particular decisions, like the installation of a new zone of equipment in the data center or operational practices and the increased cost of the electricity. In fact, electrical bills are viewed as an inevitable event that most people don’t consider trying to influence.
- Tools for modeling the electrical costs of datacenters are not widely available and are not commonly used during datacenter design.
- Billed electrical costs are often not within the responsibility or budget of the datacenter operating group.
- The electrical bill for the datacenter may be included within a larger electrical bill and may not be available separately.
- Decision-makers are not given sufficient information during planning and purchasing decisions regarding the energy cost consequences.
If the datacenter were 100% efficient, all power supplied would reach the IT loads. This would represent Power Usage Effectiveness (PUE) of 1.0. PUE is further discussed in the Green Grid white paper entitled “Green Grid Metrics.” In the real world, electrical energy is consumed by devices in a number of ways before it even reaches the IT loads. Practical requirements such as keeping IT equipment properly housed, powered, cooled, and protected is one example of how energy consumption is sidetracked, or rendered less efficient (see Figure 1). Note that all energy consumed by the datacenter in Figure 1 ends up as waste heat, which is rejected outdoors into the atmosphere. This diagram is based on a typical datacenter with 2N power and N+1 cooling equipment, operating at approximately 30% of rated capacity.
System design issues that commonly reduce the efficiency of datacenters include:
- Power distribution units and/or transformers operating well below their full load capacities.
- Air conditioners forced to consume extra power to drive air at high pressures over long distances.
- Cooling pumps which have their flow rate automatically adjusted by valves (which dramatically reduces the pump efficiency).
- N+1 or 2N redundant designs, which result in underutilization of components.
- The tradition of oversizing a UPS to avoid operating near its capacity limit.
- The decreased efficiency of UPS equipment when run at low loads.
- Under-floor blockages that contribute to inefficiency by forcing cooling devices to work harder to accommodate existing load heat removal requirements. (This can lead to temperature differences and high-heat load areas might receive inadequate cooling).
Best Practices
Right-sizing the physical infrastructure system to the load, using efficient physical infrastructure devices, and designing an energy-efficient system are all techniques to help reduce energy costs. A successful strategy for addressing the datacenter energy management challenge requires a multi-pronged approach that should be enforced throughout the lifecycle of the datacenter. The following categories of practices serve as cornerstones for implementing an energy-efficient strategy: engineering, deployment, operations, and organization.
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