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JeffHarrison
Contributor
Contributor

NTP Time Sync Issue for DC when keeping NTP on a Router.

Hello,

I've read through all of the many Time Sync issue threads but can't seem to find anything that applies to my particular environment.

I'm looking to virtualize one of my domain controllers and I'm concerned about the Time Sync issue. Most of the other threads describe having the DC get it's time sync from an ESX Host. Right now my NTP server is not a DC but it is our core router.

My questions is: Do I need to configure the ESX Host to sync it's time with the NTP (cisco) core router, or do I configure the virtual machine itself to sync with the NTP router?

Any insight would be much appreciated. Thanks!

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Erik_Zandboer
Expert
Expert

With "really busy" I mean 80% plus cpu usage. I know, with the current quadcores memory is the bottleneck in 99% of the cases, but still... I do not want my domain controller to run one minute behind... So the DC should keep his time within acceptable limits. But if it DOES get one minute behind, then what? Obviously something has failed to sync time correctly. In such cases you have a choice: do nothing and wait for the DC time to get 5 minutes behind (=end of world), or brutally fix the issue by hard adjusting the clock.... So basically the VMware timesync is only used "if all else fails"...

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Nick_F
Enthusiast
Enthusiast

We have our PDCe getting it's time externally and use Windows time replication for keeping AD sync'd and also have the ESX hosts sync time from the PDCe

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wilson94t
Enthusiast
Enthusiast

You might try enalbing something like enabling the HPET timer in the BIOS if you have one. It's not directly supported by VMware or by Windows 2003/XP, but our expierence in testing shows that a busy server combined with NTP on the guest can improve when this feature is tured on.

Secondly, if you belive that the time will skew enough that vmtools timesync is needed to bail you out, then rather than doing this, i'd prefer to adjust the peridoic interval where windows time service updates time. You can configure this with the w32tm command. you can configure this to check every few mins if required.

Here are a bunch of reg keys that you can use in order to maintain time:

http://technet.microsoft.com/en-us/library/cc773263.aspx

Why is memory the bottleneck? Are you running intel with large amounts of RAM on each VM?

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Erik_Zandboer
Expert
Expert

Hi,

Have you tested the timesync within VMs using the HPET?

You're right that it is preferred to adjust the sync interval. What I mean is that the VM should always be able to sync its time on its own (if needed by shortening the sync interval). But lets say networking somehow fails and the VMs cannot sync their clocks at all... That is more on my mind when I say "if the VM fails to sync"... But yes, the VMware timesync should always be a last resort.

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