HP ML150 HP Power Capping and Dynamic Power Capping for ProLiant servers techn - Page 25

of the server. Because of these potential conflicts, best practice is to use power caps that are at least halfway between the minimum and maximum power consumption for a server or server group. Both the iLO and IPM interfaces provide a warning whenever a power cap is set to a value lower than this. Enclosure Dynamic Power Capping has resolved this issue by disallowing enclosure power caps that are too close to the aggregate minimum power for the enclosure and its server blades. Peak power reporting and Dynamic Power Capping Both iLO 2 and IPM report the power metrics for ProLiant servers, including peak power consumption. The power monitoring system for servers records peak power consumption as the largest half-second power measurement in a 5-minute period. Although Dynamic Power Capping is much faster than basic Power Capping, it can still take up to one-half second to bring a server's power consumption back below the cap. As a result, it is possible to see peak power numbers reported that are several watts above a server's power cap value. Dynamic Power Capping still provides circuit protection, since it will always bring server power consumption below the cap long before a circuit breaker can trip. Using HP Power Regulator in conjunction with power capping Power capping and HP Power Regulator use the same underlying power management system to manage and control server power consumption. However, these two power management features are designed to accomplish different goals. Power capping provides strict control of a server's maximum power consumption. It allows an administrator to set and maintain a limit on a server's maximum power consumption across a wider power range and without explicit regard to the impact on system performance. Power capping can use both processor P-states and clock throttling to limit system power consumption. Power Regulator is focused on optimizing power use in a server (or group of servers) without impacting server performance. In its recommended configuration, Power Regulator dynamically selects the most power-efficient processor P-state that matches the present workload of the server. By doing this, Power Regulator lowers power consumption without affecting system performance or throughput. In this sense Power Regulator is primarily an efficiency tool. Power Capping and HP Power Regulator can be used on an individual server or on a server group at the same time without creating a conflict. As long as a server's power consumption remains below the power cap setting, Power Regulator is free to manage the server using its settings and P-states. Power capping will override Power Regulator only if power consumption exceeds the established power cap. Power capping and CPU utilization Both power capping and Power Regulator involve manipulating the system CPU at a very basic level. As a result, power capping can affect CPU utilization numbers reported by monitoring tools at the operating system level. If a server under a relatively constant workload is assigned a power cap low enough to engage the power control mechanisms, monitoring utilities will generally report a greater CPU utilization number than they would if the cap were not in place. 25