Technology with the Environment in Mind

Dynamic Data Center Power Management: Trends, Issues, and Solutions

POWER MANAGEMENT REQUIREMENTS FOR SERVER PLATFORMS

In this section, we identify the server requirements that address the issues of data center power and cooling efficiency, power allocation, and power provisioning.

Power Measurement Requirements

Actual power consumption for each server must be measurable at any point in time. This allows a power-monitoring module to collect power consumption data for each server and aggregate power-usage values at the rack and data center levels over a period of time.

Real-time power monitoring will allow data center managers to see the trend of power usage over time. This allows her to identify key values such as minimum, typical, and peak usage. This information is very useful in planning for future expansions, in identifying where there might be power and cooling constraints, and in locating areas where new servers can be deployed without violating power and cooling constraints. In addition, the minimum, typical, and peak values can be used to determine an appropriate power policy for each rack and hence each server in the rack. System power can be monitored by communicating with power supplies that support the Power Management Bus (PMBus) interface [13].

It is also desirable to monitor the power consumed by server subsystems: CPU, memory, fans, disks, etc. As shown in [8] an understanding of subsystem power consumption characterization for workloads can be valuable for power adaptation. Hence, subsystem power monitored values can be used for intelligent fine-grained power control and optimization algorithms.

Power monitoring eliminates the usage of nameplate or derated power value to determine the number of servers for each rack. Visibility into actual power consumption values allows IT personnel to determine the optimal number of servers to deploy per rack.

Power Control Requirements

As mentioned above, the ability to monitor server power consumption is in itself useful for power and cooling capacity planning purposes. But another key reason for monitoring power consumption is to determine appropriate power policies that can be set for servers in a data center. Such policies can be enforced autonomously in the platform, by following the platform as a service model described in [2].

One important power policy is power capping. In their study of power usage at a large Internet services data center at Google, Fan et al. [1] found that power capping offers two advantages: first, it acts as a safety valve by protecting the power distribution hierarchy against overdraw; and secondly, it enables effective usage of the available power, thereby increasing rack population. As such, dynamic power capping is a primary power control requirement that must be addressed by a power management solution.

Power Usage Reporting Requirements

To monitor power and dynamically allocate/reallocate power in a data center, a standard interface must exist between data center management software and the server being managed to do the following:

• Monitor actual power consumption over a planning period to understand historical usage patterns for capacity planning.
• Provide current as well as peak power, minimum power, and average power over an interval.
• Notify the higher-level management system if the power policy cannot be enforced.
• Send alerts to higher-level management if a certain power threshold is reached.

Regulation Requirements

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) publishes a guideline for providing the data needed for designing and provisioning a data center [9, 10]. A PM's power usage reporting capability should support this requirement. A PM can be an instrumental piece of monitoring carbon credit/generation. As carbon generation may have caps and limits in the future, a PM will be a fundamental tool to monitor and track power use, which is correlated to carbon generation. The Green Grid—a consortium of information technology companies and professionals seeking to improve energy efficiency in data centers around the globe—is developing the most advanced metrics for data center efficiency [11, 12], and the power management technology should support these reporting requirements.

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