dimanche 20 janvier 2013

[Windows 8] Power consumption, battery and WoL

I recently have to solve an issue concerning Wake on Lan with Computers using Windows 8.

You certainly know that you can use that feature for a long time to turn on your computer at home or, in a company with SCCM, in order to deploy KB, applications or OS.

However, it seems that this feature no longer works on computers with Windows 8.

Microsoft explains the reason is a "Fast Publish" article : http://support.microsoft.com/kb/2776718

With Windows 7, even if your computer is totally turned off (Classic Shutdown - S5), your network card can still use power in order to be armed and wake your computer.
On the contrary, with Windows 8, default shutdown behavior puts the system into hybrid shutdown (S4) and Network adapters are explicitly not armed for Wake-On-LAN because users expect zero power consumption and battery drain in the shutdown state.

Article provide a (not recommended) workaround to disable hybrid shutdown (S4) in Windows 8:
- Open the Power Options in Control Panel
- Select “Choose what the power buttons do”
- Uncheck “Turn on fast startup (recommended)"
- Select "Save Settings"

We arrive to that conclusions:
- With Windows 7, if you enable wake on lan on your laptop, your device still use power, even if you shutdown your device.
- With Windows 8, you must do a choice between Wake on Lan and "Fast Start Up" + Zero power consumption.

Also my recommendation are to:
- Disable WoL explicitly on your computers if you don't use that feature. Moreover, that prevent your computers to be turned on during the night because network card detected a strange packet (I ever see that...)
- If you need that feature, you can enable it on your desktop. However, it's important to look for impacts for users at start up. You can use performance tools in ADK to get relevant information.
- It is really not recommended to enable that feature on laptops and tablets. It is certainly important to contact your devices manufacturer to get information about power consumption in order to identify impact on the autonomy.

See you soon

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