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 rack power capacity (specified by the user when the rack is added to the
Dell OpenManage Power Center system) and rack power consumption (determined by the actual power
consumption of PDUs added or associated with the rack).
• Demand: Amount of power a device requests to accommodate its workload.
Dynamic power caps 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 more 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 error event
occurs for the policy. If this occurs frequently, reconsider your power allocations, or adjust workloads
accordingly.
• If fluctuations in device power requirements occur after the power cap is successfully established, then a
device that requires more 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 is applied to the device.
• If there is excess available power (known as headroom) after all power capping requirements are met, the
excess power 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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