10 power-saving myths debunked

Is powering a server off and on bad for the system? We disprove this legend and others

Myth No. 7: Notebook batteries just wear out. There's not much you can do to make them last longer.

Fact: Many laptops with nickel-cadmium batteries come with a battery-reconditioning utility that drains the battery fully, then brings it back to a full charge. Laptops with lithium-ion batteries aren't afflicted with the same memory problem as those powered by NiCad batteries. However, unlike NiCad batteries, lithium batteries prefer to be only partially discharged: Running them all the way down will shorten their life span. The calibration utility for lithium batteries actually just recalibrates the capacity measurement to reflect the loss of capacity over time; it doesn't affect actual battery life. Battery life for either type of battery can be prolonged greatly by removing the battery when the unit is plugged into AC power. This approach is recommended if your laptop supports it and power outages are infrequent in your area.

Myth No. 8: Flash SSDs (solid-state drives) reduce the amount of power consumed by a laptop.

Fact: You may or may not experience a reduction in power consumption if your system is equipped with an SSD. It will vary greatly depending on the application. Typical office applications that don't constantly access the hard drive will show very little additional battery life with an SSD installed. Software that streams data from the drive constantly, such as video applications, will show greatly increased battery life. Other power savers such as LED backlighting can save more energy in typical applications.

Myth No. 9: Going to DC power will inevitably save energy.

Fact: Going to DC power entails removing the power supplies from a rack of servers or all the servers in a datacenter and consolidating the AC-DC power supply into a single unit for all the systems. Doing this may not actually be more efficient since you lose a lot of power over the even relatively small distances between the consolidated unit and the machines. New servers have 95 percent efficient power supplies, so any power savings you might have gotten by going DC is lost in the transmission process. Your savings will really depend on the relative efficiency of the power supplies in the servers you're buying as well as the one in the consolidated unit.

Myth No. 10: You're bound to save money by rushing out and buying the most energy-efficient equipment as soon as possible.

Fact: Savings realized by more efficient equipment have to be balanced against the cost of running the existing equipment. Replacing US$5,000 servers before their end of life to save US$30 per year in power is not going to save money.

Instead, look for ways to implement energy-saving strategies that don't require new equipment or user buy-in. For example, applying a policy through Active Directory to shut down systems that aren't in use after business hours doesn't require buying new equipment and will save a lot of money. If you can get user buy-in, other actions such as powering off monitors, PCs, printers, and the like will save lots of power without buying anything.

Mario Apicella, Brian Chee, and Tom Yager contributed to this article.

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Logan G. Harbaugh

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