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An administrator can set the enclosure power cap to any value between the lowest total power consumption and the
maximum available power for the enclosure. Adding these values yields the lowest reasonable power cap
maintainable for the enclosure under all operating conditions:
•
Total power that the server blades would use in their lowest power-capped state (typically about halfway between
server idle and server maximum power)
•
Maximum power that fans in the enclosure could draw
•
Power-on power requests from the other elements in the enclosure
The maximum available power for the enclosure is the total power available from the enclosure power supplies.
Operation of Enclosure Dynamic Power Capping
Once an administrator sets an enclosure power cap, the enclosure OA monitors and maintains the cap. The OA
cannot control the power consumption of unmanaged elements in the enclosure (fans, switches, and others). The OA
maintains the overall enclosure cap by monitoring and managing the power consumption of the server blades. To
accomplish this, the OA collects the overall enclosure power use and the total power used by the managed server
blades. From this data, the OA constructs a blade power budget representing the amount of power that the blades
can consume while keeping the overall enclosure power consumption below the enclosure cap. As a final step, OA
software actively adjusts the power caps of the individual servers so that the total matches the enclosure power
budget. This process repeats every 20 seconds to maintain the enclosure power cap. As Figure 4 illustrates, the OA
increases the blade power budget and the power caps for the individual server blades if power consumption of the
unmanaged elements in the enclosure decreases.
Figure 4.
Power budgeting in Enclosure Dynamic Power Capping
Blade Power
Budget
Power used
by unmanaged
elements
Enclosure
Dynamic
Power Cap
Power Cap
Lower Bound
Enclosure
Dynamic
Power Cap
Time A
Time B
Enclosure Dynamic Power Capping
Power Budgeting
Power Cap
Lower Bound
