HP Insight Control Power Management 7.0 User Guide

While the enclosure may theoretically consume 35A of power (the Calibrated Max Power based
upon the current configuration of the hardware), the maximum power observed since power
management monitoring commenced was only 14A (Peak Observed Power). The difference of
Calibrated Max Power and Peak Observed Power, 35A-14A = 21A, represents the potential
power that can be reclaimed when applying the power cap value. Power caps are supported on
both BladeSystem enclosures and many models of HP ProLiant servers. Using a Dynamic Power
Cap value prevents the capped device from using more than the specified amount of power – even
if it involves reducing the performance of the system.
Various HP ProLiant servers support power capping (which limits the thermal output), and Dynamic
Power Capping (which limits the electrical power consumption). If you are attempting to reclaim
thermal capacity, or limit the total heat output of a group of systems, then either type of cap may
be used. If, however, you are attempting to prevent an electrical overload, be sure that your device
supports dynamic power capping.
Similarly, for example, consider a system say ProLiant ML370 server as shown below:
Figure 7 Example of Power Summary Meter
While the faceplate power is 1000 Watts, the Calibrated Max Power as measured by the hardware
itself is only 509 Watts, and based upon historical observation of several months, the highest
power consumption ever observed was 432 Watts. Based on past behavior, there is 502-432 or
70 Watts that can potentially be reclaimed without noticeably impacting the performance of the
system.
When determining an appropriate cap to reclaim capacity, consider the following issues:
1. Do I have sufficient power history collected for this system to make reasonable projections for
future behavior? Several months of power history will likely ensure that you are seeing a typical
depiction. However, if your computing demand has a seasonal component (such as the
holidays, tax season, or end of the fiscal year spikes), you may want to analyze power history
covering such time periods, or allot additional headroom to avoid potential performance
impacts of the cap.
2. Applying a Dynamic Power Cap value allows sharing of the cap value dynamically from
systems that are idle to systems that are experiencing demand. But, a cap value applied to a
single system does not adjust automatically, so it is important to ensure that there is sufficient
headroom to avoid bumping into the cap when there is more demand in the future.
3. When considering the requirements for the future, what is the trend of my CPU utilization and
therefore power consumption and thermal output? Are my workloads relatively stable over
time, or is there a growing need for additional CPU? These factors dictate how much headroom
you must leave to avoid unnecessarily restricting performance.
4. Do I anticipate adding additional hardware (systems in an enclosure or memory, disks, or
add-in cards to a system)? Such additions will increase the upper end of the operating range
of the equipment.
Task: Determining trapped capacity in your data center 25