HP ML150 HP Power Capping and Dynamic Power Capping for ProLiant servers techn - Page 7

Differences between HP Dynamic Power Capping and HP Power Capping Both HP Dynamic Power Capping and HP Power Capping are designed to achieve the same general goal of maintaining a server's power consumption at or below the cap value set by an administrator. HP Dynamic Power Capping, however, monitors power consumption and maintains a server's power cap much more rapidly than HP Power Capping. Table 3 provides a quick architectural and operational comparison of HP Dynamic Power Capping and HP Power Capping. To avoid confusion between the two, HP Power Capping will be referred to as basic Power Capping throughout the remainder of this paper. Table 3. Comparison of Dynamic Power Capping and basic Power Capping Power capping executed from Control of processor power Power monitoring cycle Time to bring server power consumption back under its cap Intended application Dynamic Power Capping Power management microcontroller Direct hardware connection to processor to control Pstate/clock throttling at the processor hardware level More than 5 times per second Less than 0.5 seconds Managing power and cooling provisioning Basic Power Capping iLO and system ROM BIOS Firmware control of Pstate/clock throttling through processor registers Once every 5 seconds 10 - 30 seconds Managing cooling provisioning Power provisioning and Dynamic Power Capping Basic Power Capping does an excellent job of maintaining average server power utilization at or below a cap value. It is can be used to help manage data center cooling requirements by limiting server power consumption in a timely enough manner to prevent excessive heat generation. However, as the information in Table 3 illustrates, basic Power Capping cannot respond quickly enough to limit sudden increases in server power consumption that could cause an electrical circuit breaker to trip. Dynamic Power Capping operates more than 25 times faster than basic Power Capping, and can bring a server experiencing a sudden increase in workload back under its power cap in less than one-half second, preventing any surge in power demand that could cause a typical data center circuit breaker to trip. Dynamic Power Capping has been designed and tested to ensure that it can prevent tripping circuit breakers that have a specified trip time of three seconds or longer at 50 degrees C and 150 percent overload. This basic difference, the ability to keep server power consumption below the power cap in real time, means that Dynamic Power Capping can be used as an effective tool in planning and managing both electrical provisioning and cooling requirements in the data center. An administrator can electrically provision a PDU or a rack to something less than the full faceplate power rating of all the servers 7