Powering Your Equipment

Power Efficiency Guide

Ultimate Guide to Power Efficiency

Get Instant Access

The vast array of equipment required to operate today's data centers use a tremendous amount of electrical power. Servers, hard disk storage, memory, and even your network all require ever more expensive energy to operate. Let's take a look at each of these types of equipment and see what energy savings we can find in each.

Facility Efficiency


Servers are the top users of power of all the computer equipment in the data center and, for most data centers, the first and best place to look for energy savings. The annual energy costs for a single server can be estimated based on its rated power and the price of electricity ($0.11 per kWhr commercial average in the United States, see Figure 11-2 for power costs in your area) as shown in the following equation:

Annual power cost = 8760-X —-—— X server power in KW

yr kWhr

Once you know how much each server costs in ongoing energy costs, you know how much you can save for each server you eliminate or replace with a more energy efficient one. It's quite simple in theory, as you have only two options for reducing the amount of power used by servers:

1. Reduce the number of servers.

2. Make the remaining servers more efficient.

Of course, these goals are easier said than done. You had a very good reason for every server installed in the data center, and you probably focused on meeting the user's needs by ensuring the server had plenty of horsepower to run its applications. But because energy usage was probably not high on the priority list, what you ended up with was too many inefficient servers drawing lots of power and generating lots of heat that has added up to today's huge energy bill.

First, look at how many of the existing servers can be turned off. In most data centers, as many as 10 percent of servers are no longer actively used and can be turned off. Since idle servers still use a significant amount of power just waiting for something to happen, this wastes a huge amount of energy. Implementing a formal decommissioning process to eliminate these unused servers can realize immediate energy savings.

Another way to reduce the number of physical servers is through the use of virtualization. Server virtualization (see Chapter 10) allows you to run multiple "virtual" servers on a single physical server. Since most servers have a utilization rate of 10% to 15%, two or three virtual servers can on average be hosted on a single physical server.

The next consideration is enabling power saving features that are available on newer servers. In many data centers, power management is not a factor because administrators have historically focused on uptime and performance metrics, with little regard to the amount of energy being used. Support for power management in servers is relatively recent and should

US Electricity Costs per kWh in July 2008

US Electricity Costs per kWh in July 2008

Figure 11-2


Figure 11-2


be done with caution. Some things to consider when evaluating the use of power management are:

▲ Begin with a test environment to see how well power management works for your servers and to look for any problems. You want to have a process that is automated and still reliable.

▲ Check with your hardware provider about support for sleep and hibernate modes for servers. These functions may not work exactly as you are used to them working on desktop machines.

▲ According to Microsoft, sleep and hibernate functions are turned off automatically when using Windows Server 2003 and 2008 on machines with more than 4 GB of memory due to performance issues. Details can be found in the Knowledge Base article available at: support.microsoft.com/kb/888575.

▲ While turning servers off with scripts is easy, turning them back on can be more difficult. Check with your server vendor to see what options are available.

Power supplies are the main source of energy waste in servers. Server manufacturers are in most cases oversizing power supplies and, since power supplies are most efficient at 100% capacity, much energy is wasted. Energy efficient power supplies are 15% to 20% more expensive than the commodity power supplies used in most servers, so servers purchased with low purchase price in mind waste a lot of energy. In low-cost power supplies, efficiency peaks at about 70% to 75% when the server is 100% utilized, but drops into the 65% range at 20% utilization. Since the average server is 10% to 15% utilized, almost half the power used is wasted as heat and never reaches the rest of the server. Just by using smaller power supplies that will run closer to peak power levels where it's more efficient can save a significant amount of energy.



PG&E Corp., the San Francisco-based utility, offers a "virtualization incentive" program that pays $150 to $300 per server removed from service as a result of a server consolidation project. PG&E also offers rebates for data centers that use Sun Microsystems Inc.'s energy-friendly Niagara T1000 and T2000 servers, and for virtualization software used to consolidate servers.


Disk storage is the third largest user of power in most data centers, after cooling and powering servers. Storage in the average data center consumes 20% to 25% of the total power used. As storage needs have skyrocketed, the number of file servers and direct-attached storage devices has also increased dramatically. These devices require an ever-increasing amount of power to operate. Many are poorly utilized either because too much unused space is allocated to specific applications or on-line storage is being allocated to applications that are rarely used. Industry estimates of storage utilization rates range from 25% to 40%. This means that 60% to 75% of the storage capacity that is being powered is not being used. Compounding the problem is the fact that in many cases, storage allocated for a particular use

Figure 11-3

Was this article helpful?

0 0

Post a comment