4

Here's an interesting one I haven't seen on ServerFault I'd like to "discuss" based on our rule regarding a Good Subjective question.

I have a ton of Windows 2008/2012 VMs in my environment running under VMWare 5.1 and 5.5 clusters.

There is a setting that is pretty common on NICs that allows to you check/uncheck stating Allow the computer to turn off this device to save power. The default is for this to be checked. The concept being to help save power if the NIC isn't plugged in and shown as enabled and active in Windows (is my understanding). EDIT: the before is actually an incorrect passed down falsehood...This KB article does a better job of explaining what this setting does: Information about power management setting on a network adapter It doesn't simply turn off the device if there is some idle time.

enter image description here

Now we get into the VM world side of things.

Does such a setting have any bearing checked or unchecked on a VM? Unchecking it seems frivolous since the NIC isn't a physical device and isn't drawing any actual electrical power regardless. But does leaving the box checked having any negative affects when Windows likes to believe it is a physical device? Should all VMs have this box checked or unchecked?

TheCleaner
  • 32,627
  • 26
  • 132
  • 191
  • 1
    Are you sure this turns off a NIC if isn't plugged in to save power? If I understand http://support.microsoft.com/en-us/kb/2740020 correct this "setting controls how the network card is handled when the computer enters sleep" – Mario Lenz Mar 27 '15 at 21:21
  • @MarioLenz Interesting...I had it wrong this whole time based on passed down "knowledge"...thanks! – TheCleaner Mar 28 '15 at 01:13

2 Answers2

3

This setting only take effect when the computer goes into sleep mode. When you have a physical machine that has multiple NICs, and only 1 uses WOL, then you can save power by enabling this on the non WOL nics. If you never need WOL, this can save power. On a VM this wouldn't have any real effect.

Jim B
  • 24,081
  • 4
  • 36
  • 60
  • Jim, thanks...I'll likely accept your answer, especially based on Mario's KB article link. I'm curious why so many online (VMWare forums, etc.) talk about this setting and recommend turning it off for the VMs. Are they like me and believing a handed down old wives' tale of how it works? – TheCleaner Mar 28 '15 at 01:15
  • 1
    if I didn't know what it did, I'd probably recommend turning it off too. – Jim B Mar 30 '15 at 16:22
0

My 2¢: I've encontered issues with Windows Server 2008 and Intel NICs with Allow the computer to turn off this device to save power enabled. For some reason, the card would drop link speed from 1Gb/s to 10Mbit/s and wouldn't get back to 1Gb/s until a manual reset. Disabling this option fixed this. I doubt that it would affect VM, but I'd disable it on a host system just in case.

beatcracker
  • 1,359
  • 8
  • 13