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By Leah Schoeb, Sr. Technical Marketing Manager, VMware

Power Saving turned on in the server BIOS has been the cause of many performance issues reported in vSphere 4.1. In fact it has been the #1 resolution to performance problems reported in the past few months.  It has masked itself as performance issues with CPU, memory, network, and even storage.  Certain applications are also very sensitive to processing speed latencies may show less than expected performance when processor power management features are enabled.  Before spending many hours trying to identify performance issues check to make sure that power saving is turned off in the server BIOS and then check to see if the problem still persists.  If the problem still exists then you it would be worth it to troubleshoot the problem. 

Recent KB article – “Disabling power management usually results in more power being consumed by the system, especially when it is lightly loaded. The majority of applications benefit from the power savings offered by power management, with little or no performance impact. Therefore, if disabling power management does not realize any increased performance, it is recommended that power management be re-enabled to reduce power consumption.” (Reference below)

Disabling Hardware Power Management

Disabling processor power management in the server hardware is vendor specific. Here is an example of the HP ProLiant:

HP Power Regulator

Processor power and performance state registers exposed by processor vendors let you use HP Power Regulator to control processor power usage and performance. Power Regulator directly adjusts the frequency and core voltage of ProLiant server processors.

Using Power Regulator, you can configure a server to maximize performance, maximize power savings, or match processor power consumption dynamically as system load changes. This lets you maintain an optimal balance of performance and power utilization under all operating conditions.

  • HP ProLiant servers with the HP Power Profile option (ProLiant G6 or greater)

    Review both the HP Power Profile and HP Power Regulator Mode in the BIOS settings.  For HP Power Profile, you see these options:

    • Balanced Power and Performance (default)
    • Minimum Power Usage
    • Maximum Performance
    • Custom

Choose Maximum Performance to disable power management. If Custom is already selected, refer to the Power Regulator Mode options below.  If you choose Custom, set the HP Power Regulator Mode to OS Control Mode.

  • HP ProLiant servers without the HP Power Profile option

    Review the Power Regulator Modes in the BIOS settings. You see these options: 

    • HP Static High Performance mode
    • HP Static Low Power mode
    • HP Dynamic Power Savings mode (Default)
    • OS Control mode

Choose HP Static High Performance mode to disable power management. If OS Control mode is selected, refer above for disabling power management within the OS.

More about the HP regulator you can go to:  http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00300430/c00300430.pdf

Additional information, like disabling ESXi power management was recently posted in a kb article at:  http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1018206