ESX/ESXi provides up to four power management policies. You choose a power management policy depending on a host's hardware characteristics and BIOS support, which allows you to configure servers for specific levels of power efficiency and performance.

To improve CPU power efficiency, ESX/ESXi can take advantage of performance states (also known as P-states) to dynamically adjust CPU frequency to match the demand of running virtual machines. When a CPU runs at lower frequency, it can also run at lower voltage, which saves power. This type of power management is typically called Dynamic Voltage and Frequency Scaling (DVFS). ESX/ESXi attempts to adjust CPU frequencies so that virtual machine performance is not affected.

When a CPU is idle, ESX/ESXi can take advantage of power states (also known as C-states) and put the CPU in a deep sleep state. As a result, the CPU consumes as little power as possible and can quickly resume from sleep when necessary.

Table X shows the available power management policies. You select a policy for a host using the vSphere  Client. If you do not select a policy, ESX/ESXi uses High Performance by default.

CPU Power Management Policies

Power Management Policy

Description

Not supported

The host does not support any power management features or power management is not enabled in the BIOS.

High Performance (Default)

VMkernel detected certain power management features, but will not use them unless the BIOS requests them for power capping or thermal events.

Balanced Performance

VMkernel is using all available power management features to reduce host energy consumption without compromising performance.

Low Power

VMkernel aggressively uses available power management features to reduce host energy consumption at the risk of lower performance.

Custom

VMkernel implements specific user-defined power management features based on the values of advanced configuration parameters. The parameters are set in the vSphere Client Advanced Settings dialog box.