10 power-saving myths debunkedCompanies are finding themselves embroiled in a power crisis as they struggle to find ways to rein in soaring energy costs as well as do their part to address global climate change
By Logan G HarbaughCompanies are finding themselves embroiled in a power crisis as they struggle to find ways to rein in soaring energy costs as well as do their part to address global climate change. However, how can one be certain that the power-saving strategies that his company has adopted are, in fact, the best ones? After all, there are plenty of myths out there about saving energy that are deliberately false. In this report, 10 such myths are examined and bring the truth to light.
Myth : Powering a computer or server up and down, limits its life span. The extreme temperature and current swings of power cycling can stress electronic components in a machine.
Fact: Power cycling healthy electronics is not a source of stress. The same electrical components that are used in IT equipment are used in complex devices that are routinely subjected to power cycles and temperature extremes, such as factory-floor automation, medical devices, and your car.
There is a kernel of truth in this myth; however, cycling power on a sick system is going to bring attention to latent component weaknesses that go unnoticed in operation. Power-on diagnostics are brief yet rigorous and can be performed remotely on servers with dedicated management controllers. Power cycling doesn't just save energy but it's a zero-cost aid to maximising server availability.
Myth : It takes too long to cold-start servers to react to spikes in demand. If customers are made to wait, they'll go elsewhere.Fact: Idling servers at zero workload as hot spares is an egregious waste of energy and an administrative burden. If customers need to wait while you spin up cold spares to handle rising workload, brag about it. For a website, put up a static page asking users to wait while additional resources are brought online. As for the wait, people will stay on hold if they know their call will be answered. Build power management into your services architecture and make it part of the message that you send to users and customers.
You can also select systems that cold-boot rapidly. This metric isn't usually measured, but it becomes relevant when you control power consumption by switching off system power. Servers or blades that boot from a snapshot, a copy of RAM loaded from disk or a SAN can go from power-down mode to work-ready in less than a minute.
Myth : The power rating (in watts) of a CPU is a simple measurement of the system's efficiency.
Fact: Efficiency is measured in percentage of power converted, which can range from 50 to 90 percent or more. The AC power not converted to DC is lost as heat, which increases the cooling burden of the system, adding even more to the overall energy loss. Unfortunately, it's often difficult to tell the efficiency of a power supply, and many manufacturers don't publish the number. You can either look for systems with published efficiency numbers or measure the actual power draw of various systems at idle and full load, then make your decisions based on that.
Myth : It's better to pack one big server with all the RAM, CPUs and peripherals, it can hold rather than to use multiple smaller servers.
Fact: This is only true if the big server is fully utilised, which can be dangerous with critical applications. Multiple smaller servers can be powered off or put in suspend mode when not in use, and they are safer from a redundancy point of view.
Myth : LCD monitors use a trivial amount of power, so you might as well leave them on. Their colours and backlight brightness improve with warm-up time.
Fact: The average 17-inch LCD monitor consumes 35 watts of electricity. Adding together the hundreds of LCDs in an enterprise, the power used may not be that trivial. Energy Star LCD monitors will power down to sleep mode if the PCs' power management software is set up to tell them to. This saves energy and money as well.
Myth : A notebook doesn't use any power when it's suspended or sleeping. USB devices charge from the notebook's AC adapter.
Fact: Sleep (in Vista) or Hibernate mode in XP saves the state of the system to RAM and then maintains the RAM image even though the rest of the system is powered down. Suspend saves the state of the system to hard disk, which reduces the boot time greatly and allows the system to be shut down. Sleeping continues to draw a small amount of power, between one and three watts, even though the system appears to be inactive. By comparison, Suspend draws less than one watt. Even over the course of a year, this difference is probably negligible.
Myth : 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, and 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.
Myth : 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 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 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 : 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 data-center 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 : You're bound to save money by rushing out and buying the most energy-efficient equipment as soon as possible.
Fact: Savings realised by more efficient equipment have to be balanced against the cost of running the existing equipment. 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 etc, will save lots of power without buying anything.
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