10 IT Power-Saving Myths Debunked

snydeq writes "InfoWorld examines 10 power-saving assumptions IT has been operating under in its quest to rein in energy costs vs. the permanent energy crisis. Under scrutiny, most such assumptions wither. From true CPU efficiency, to the life span effect of power-down frequency on servers, to SSD power consumption, to switching to DC in the datacenter, get the facts before setting your IT energy strategy."

Comments

Sleep != Hibernate

[Taimat]

Myth No. 6: 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 1 and 3 watts, even though the system appears to be inactive. By comparison, Suspend draws less than 1 watt. Even over the course of a year, this difference is probably negligible.

um... Hibernate != Sleep. Hibernate in XP saves the RAM to the Hard Drive, and powers off. Suspend keeps RAM powered....

Re:Sleep != Hibernate

[afidel]

How about build an energy efficient PC! I have a LP AMD 64 x2 with a Geforce 7600GS, 2 HDD's, 2GB of ram and a TV tuner and an 85% efficient PSU and I peak at around 150W, using 140W at idle is insane. For the next generation of games I'm thinking about upgrading to a 9600 GSO but that will up my idle and peak numbers by at 20W so I'm holding off till I get a game that really needs it.

Re:Sleep != Hibernate

[644bd346996]

http://anandtech.com/casecoolingpsus/showdoc.aspx?i=3413

Even though the article is about power supplies, it has quite a bit of information about how much power various components draw.

Re:Sleep != Hibernate

[tknd]

For the record, my system pulls 120 W idle, 230 running CoHOF, and 5 in S3. It is extremely overclocked and mostly older components which tends to skew things, but I'm looking to upgrade and wouldn't mind saving a few bucks in energy costs in the long term.

5 watts in S3 is pretty bad in my book. Disconnect all USB devices and check again what your S3 power consumption is. If it is still high, most likely the PSU you have is not efficient. It could also come from other things like the motherboard, but most of the time it is the PSU. If your system idles at 120w, and 230w during load, you might be able to run with as low as a good 350w rated PSU. For example if your current PSU was around 70% efficient and you replaced it with an 80% efficient one, then during load your 230w draw would drop to around 201w. But you'll have to check and see if you can find the efficiency numbers for your current PSU.

How do you tell how much power a component is going to pull before you buy it?

There's no single source, but there are some useful websites.

80plus.org
Silent PC Review They generally provide both noise and power consumption measurements in their reviews
Silent PC Review Forums More anecdotal but at this point it is still good data. Many users post their own tests and measurements on the boards. It helps you get an idea of what's achievable and what isn't. There are also some nicely compiled charts that combine data from difference sources. I find the numbers are sometimes inaccurate but not too far off.

Re:I dunno..

[Nursie]

That depends if your system has been tuned to boot in 5 seconds.

Or if it can return from suspend-to-ram nice and quick.

Re:I dunno..

[Anonymous Coward]

If you're booting those servers diskless with PXE and NFS, the boot time should be negligible. I should imagine the trick would also be to bring additional resources online before you are the point that you must tell users to wait while the server boots. The magic would be in predicting near-term future use...

Single page

[gnick]

Sorry for the thread hijack, but I decided to post this link as soon as I saw the links to all 4 pages of the top 10 list.
http://www.infoworld.com/archives/emailPrint.jsp?R=printThis&A=/article/08/10/06/40TC-power-myths_1.html

Re:Questionable grasp on the problem space.

[Anonymous Coward]

I like how this plays with the following assertion filed under "Myth No. 9: Going to DC power will inevitably save energy."

"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."

So, when it suits his argument, power supply efficiencies range from 50-90% efficency, and are kept hidden by manufacturers. Then, when that doesn't suit his argument, all of a sudden power supplies are at least 95% efficient, and everyone knows that.

I call shenanigans!

Re:I dunno..

[gnick]

FTA:

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.

They must be using a different version of XP than I am... When I 'Hibernate' my laptop, it dumps the RAM to a file on the hard drive and then powers off completely. When I 'Stand By' my system, it keeps everything in RAM.

Maybe they have SP4...

Re:I dunno..

[snowraver1]

If you are using electric heat, chances are you don't live in a cold climate and pay for air conditioning for much of the year negating any "savings". Here in cold-balls Canada, EVERYONE has centeral heating; it's too expensive to use electricity. That being said, I do agree that datacenters' heat should be used to heat useful things (office bldgs, like you suggest).

Re:Google

[Animats]

Google developed their own power supply

Actually, Google's point was that they wanted motherboards that ran on 12 VDC only. PC power supplies are still providing +12, -12, +5, -5, and +3.3v. Most of those voltages are there for legacy purposes, and DC-DC converters on the motherboard are doing further conversions anyway. So there's no reason not to make motherboards that only need 12 VDC. Disks are already 12 VDC only, so this gets everything on one voltage. This simplifies the power supply considerably, and avoids losses in producing some voltages that aren't used much.

But Google wasn't talking about using 12 VDC distribution within the data center. The busbars required would be huge at such a low voltage. They were talking about using 12 VDC within each rack. Distribution within the data center would still be 110 or 220 VAC.

Re:I dunno..

[compro01]

I know a total of 5 people who don't use natural gas for heating, and 4 of them use propane as they're so far out of the way the gas network doesn't reach them. only 1 guy uses non-central (heating controlled on a room by room basis) electric. In terms of raw dollars-per-joule, gas is a way better proposition. even after the latest electric rate jump (from 6 cents to 9 cents per KW-hr), gas is still about 1/3 the cost of electric heat.