HP Dynamic Power Capping

Typically, processors are responsible for about one-third of the power consumed by a server. This means that the processor indirectly drives the power consumption and heat generation of other server components. By controlling the processor’s power use, administrators can control the entire system’s power requirements. HP Dynamic Power Capping technology takes advantage of this processor- driven model and controls overall server power consumption using two separate mechanisms: changing the processor performance state (P-state) and throttling the processor clock.

HP Dynamic Power Capping uses sophisticated monitoring and control circuitry to safely limit maximum server power consumption to a preset level. Because it is hardware-based, Dynamic Power Capping can control server power consumption quickly enough (less than half a second) to ensure that sudden surges in power demand from the servers are quickly managed and will not trip circuit breakers. 2 This allows an administrator to electrically provision a power distribution unit (PDU) or a rack to something less than the combined faceplate power rating of all the servers in the rack.

The first step in power capping is to measure the server’s power use with Systems Insight Manager or Insight Power Manager (IPM)—note that only IPM monitors server power over time. Administrators can set Dynamic Power Caps for individual servers from the iLO 2 user interface when using an iLO Advanced Pack license. Using IPM, administrators can also set power caps for groups of ProLiant ML and DL servers and for groups of BladeSystem enclosures. To set a power cap for an individual enclosure, the administrator can use IPM or iLO 2.

To control the power use of a group of servers, IPM separately sums the minimum power use, maximum power use, and power supply ratings of all servers in the group. IPM then displays these three totals in a graphic user interface. The interface allows an administrator to apply a group power cap that is between the total minimum power use and the total power supply rating of the servers. Then IPM assigns each server a proportion of the group’s total power. These individual power caps will remain in place until they are changed through the IPM or HP iLO Advanced interfaces.

Power capping has even more options in the HP BladeSystem. Enclosure Dynamic Power Capping is a special implementation designed specifically for HP BladeSystem enclosures. Enclosure Dynamic Power Capping monitors the workloads of the individual server blades and then reapportions the individual power caps of the servers after a predetermined monitoring cycle. This allows the busiest server blades to draw more of the total enclosure power.3

Sea of Sensors

Servers use internal fans to exhaust heat into the data center to keep their components operating within a safe temperature range. Previous generations of servers used temperature sensors and a “fan curve” to set the speed of the fans to a preset value based on the measured temperature. The Sea of Sensors technology in ProLiant G6 servers uses up to 32 separate sensors to more accurately map the temperature profile inside the server. Instead of using a simple fan curve, ProLiant G6 servers contain a controller that uses a proprietary feedback algorithm to continuously adjust individual fan speeds. This improved monitoring technology prevents overcooling within the server and lowers the overall power consumed by the fans.

2Dynamic 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° C and 150 percent overload.

3For more information on HP Dynamic Power Capping, go to http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01549455/c01549455.pdf.

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