Understanding Power Management Enhancements in Windows Server 2008 R2

Thursday Mar 18th 2010 by Jabez Gan

With the ability to park idle cores and budget power consumption, Windows Server 2008 R2 could provide a lot of energy savings in your datacenter.

One of the key enhancements found in Windows Server 2008 R2 is power management. Inefficient power management can increase power consumption, thus increasing the overall operational cost in an organization. Inefficient power management can contribute to one of the more expensive costs in an organization, especially when multiple server farms are involved.

So what has Windows Server 2008 R2 has to offer in terms of Power Management enhancements? Let's step back and talk more about the fundamentals of power management.

Why Power Management

As more servers are being deployed, not all will be fully utilized. You might argue that the future is virtualization, which will consolidate operating systems into a single physical server and increase utilization. However, if new servers are to be deployed, these new servers will usually take a while before reaching full utilization. The next question is: How much power will we be wasted on the underutilized servers?

Power consumption scales linearly with CPU utilization

As shown in figure 1 above, assuming a server uses a minimum of 200W of power just to be powered on, as CPU utilization increases, the power consumption increases. If multiple servers with low CPU utilization are powered on, each of them will be using a minimum of 200W power consumption while not doing any real work.

This is why Microsoft has made an extra effort on power management for Windows Server 2008 R2. But before we talk about power management enhancements of Windows Server 2008 R2, let's step back and re-introduce you to power management on Windows Server 2008.

Power Management in Windows Server 2008

Windows Server 2008 and Windows Vista incorporated a few enhancements into power management. One major change was the implementation of processor power policy. Processor power policy allows the operating system to switch off the extra processors which are not in use to conserve energy. The power policy includes values to set the minimum and maximum allowable range of performance states, which is shown in figure 2 below.

Power options for Vista

With Windows Server 2008, it is possible to define the minimum and maximum percentage of processor state. Processor state is based on CPU usage and other factors, depending on the processor power management features. By modifying the processor state, the power consumption can be lowered, potentially saving tremendous amounts of power in a data center. If you are wondering how it works in earlier version of operating systems, they rely on dynamic throttling policies for the processors.

This setting can also be pushed down by using group policy for Windows Server 2008 and Windows Vista operating systems.

Power Management in Windows Server 2008 R2

Power management is further enhanced in Windows Server 2008 R2, which includes key features like Core Parking, power metering and budgeting, and remote power management through WMI.

Let me further explain the 3 key features that you need to know:

  • Core Parking: With the multi-core-processor servers being sold nowadays, not all processor cores will be fully utilized most of the time. With Core Parking, if all cores are under low utilization, the processing will get moved to a single core, allowing the other cores to sleep. As processing demand increases, more cores will get called up to assist in the additional processing demand. Windows Server 2008 R2 supports up to 256 cores, and it will be a huge performance benefit as more cores are installed on the server.
  • Power Metering and Budgeting: Power metering and budgeting infrastructure promotes energy efficiency on computer systems by providing power consumption and management features. Power meter allows the monitoring of how much power a computer system or subcomponent need to use. Power budget is used to determine a power limit that is supported on a computer system. Some hardware supports the overwriting of the configuration of the power budget. From Windows Server 2008 R2 and Windows 7 onward, developers or system integrators are able to tune their system or applications so that it is balance between power and performance.
  • Remote Power Management through WMI: Power management can be configured through group policy or by using Windows APIs as explained above, but let's not forget about the remote administrators. Through Windows Management Instrumentation (WMI), it is now possible to configure power management through WMI locally or remotely. This means that administrators can execute scripts on Windows Server 2008 R2 or Windows 7 on the fly.
  • Figure 3, below, shows an additional power option which is available as part of Windows Server 2008 R2 and Windows 7:

    Power options for Windows 7


    These features might look insignificant to you, but if multiple servers are involved, or if you manage servers across the entire data center, creating scripts and applications to tweak the power management features of the operating systems is going to create a big savings as part of the operation costs.

    This article has covered on power management enhancement which is introduced in Windows Server 2008 R2. Our next article will cover the new and improved management consoles, which help administrators do more with less time.

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