Owner's Manual

Dynamic Power Caps
The following terms are helpful for understanding how a dynamic power cap works:
• Consumption: The amount of power a device is using.
• Power Cap: The maximum amount of power that a device is allowed to consume (may not be equal to its
demand).
• Headroom: The difference between power cap and power consumption of a device or a group of devices under
a power policy.
• Demand: Amount of power a device requests to accommodate its workload.
The top priority of a dynamic power cap is to enable all devices to execute workloads without requiring more power
than the overall power cap assigned to the group. When choosing a dynamic power cap, remember:
• If lower-priority devices require additional power to maintain their cap, they may receive more power than
higher-priority devices.
• If the power cap is too restrictive and the group power consumption exceeds the power cap, an event is sent for
the power policy. If this occurs frequently, you should reconsider the power allocation or adjust workloads
accordingly.
• If fluctuations in device power requirements occur after the power cap is successfully established, then a
device that requires additional power may not receive it if the power cap of another device in the policy would
be violated. To force one or more devices in a policy to a lower cap, create a static power policy for the device
at a lower level (rack or chassis). The most restrictive power cap of the overlapping policies will be applied to
the device.
• If there is excess available power (known as headroom) after all power capping requirements are met, it is
dynamically allocated according to the priority and demand of each device in the power policy.
Power Policy Capabilities
Power Center defines the following statuses of power policy capabilities for the devices:
• Unknown — Shown for unsupported devices or devices that were never connected to Power Center.
• None — No power policy capability. You cannot set any policy on the device.
• Monitor — With power monitoring capability only.
• Monitor & Capping — With power monitoring and capping capabilities.
• Monitor and Upgradable — With power monitoring capability, and can be upgraded to have power capping
capability.
You can find this power policy capability status in the Power Capability column of the Devices page.
For servers that comply with Dell iDRAC7, when there is a power policy capability change due to a license change,
Power Center will change its information in the management console within 24 hours. There are two scenarios:
Scenario 1 — The license expires or is not imported
In this case, the following happens:
• If a policy exists on the devices, you will receive a "Server Capabilities Changed" event.
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