The power requirement required by data centers and network rooms varies on a minute by minute basis depending on the computational load. This magnitude of this variation has grown and continues to grow dramatically with the deployment of power management technologies in servers and communication equipment. This variation gives rise to new problems relating to availability and management.
Dyna mic Power
Variations in Data
Centers and
Network Rooms
By Jim Spitaels
White Paper #43
Revision 2
Executive Summary
The power requirement required by data centers and network rooms varies on a minute by
minute basis depending on the computational load. This magnitude of this variation has
grown and continues to grow dramatically with the deployment of power management
technologies in servers and communication equipment. This variation gives rise to new
problems relating to availability and management.
?2005 American Power Conversion. All rights reserved. No part of this publication may be used, reproduced, photocopied, transmitted, or stored in any retrieval system of any nature, without the written permission of the copyright owner. www.apc.com Rev 2005-2 2Introduction
Data centers and network rooms draw a total electrical power, which is the sum of the power consumed by the installed Information Technology equipment. Historically, this equipment consumed power at a value that varied only slightly depending on the computational load or the mode of operation. The notebook computer created the requirement that processor power be managed to lengthen battery run time. Power Management technology enabled the power consumption of laptop computer processors to be reduced by up to 90% when lightly loaded. As this technology has matured it has begun to migrate into server design. The result is that newly developed servers can have a power consumption that varies dramatically with workload over time. When power varies with time, a variety of new problems occur for the design and management of data centers and network rooms. A few years ago, this problem was negligible. The problem has now reached a point where it is significant and the magnitude of the problem is growing. Fluctuations in power consumption can lead to unplanned and undesirable consequences in the data center and network room environment; including tripped circuit breakers, overheating, and loss of redundancy in redundant power systems. This situation creates new challenges for people designing or operating data centers and network rooms.
Magnitude of Dynamic Power Variation
Through the 1990's, almost all servers drew a nearly consistent amount of power. The primary drivers of power variation in servers were related to disk drives' spin-up and speed changes in temperature controlled fans. The computational load placed on processors and memory subsystems caused a negligible variation in overall power consumption. On a typical small business or enterprise servers, the total power variation was on the order of 5% and was almost independent of the computational load. Significant reductions in power consumption require cooperation between the BIOS, chipset, processor, and the operating system. In such a power managed system, whenever the processors are at less than 100% utilization, the operating system will execute an idle thread which will cause the processors to enter a low power state. The amount of time spent in the low power state is inversely proportional to the computational load on the system (e.g. a processor that is operating at 20% CPU utilization will spend 80% of it's time in a low power state). The techniques used to achieve low power states vary among vendors and processor families but the most common techniques involve reducing or stopping clocks and removing or reducing voltages applied to various parts of the processor, chipset and memory.
?2005 American Power Conversion. All rights reserved. No part of this publication may be used, reproduced, photocopied, transmitted, or stored in any retrieval system of any nature, without the written permission of the copyright owner. www.apc.com Rev 2005-2 3Recently, processor vendors have introduced techniques to conserve power while the CPU is actively performing work. These methods involve changing the frequency of the clocks and the magnitude of the voltages applied to the processors to better match the workload applied to the processor in the non-idle state. It is important to note that any technique which conditionally reduces processor power only reduces the average power consumed by the system; the maximum power remains u... [download for more]
