Windows Time in Guest OS

I followed KB1339 to get the ESX host syncing time with an NTP host. Infact, it's pointed to the same place our domain PDC emulator is pointing.

The article says that after you configured VMWare Tools to sync time with the ESX host, you should disable the windows time service. My question is, is this part necessary? My co-worker seems to think that the VMWare tools time sync will override the windows time service so disabling it isn't necessary. I'm not convinced that's true. Any thoughts?

Hi,

If you enable the time synch with VMWare Tools, you can disable windows service. The windows service use NTP protocol, and by this way, synchrosize on the network. VMWareTools, doesn't use NTP server but use internal protocol to comunicate with ESX server. The ESX server use NTP protocole.

If you use both (VMWare Tools and Windows Service) you can have 2 ways to keep you VM on time : Domain and ESX. It can create some special effect (too much time synch, time synch very long, ...). If VMWare Tools works correctly, it should desactivate the possibility to your VM to synchronize with the domain. I didn't check this point.

My point of view, the windows time service should running and don't use VMWare Tools because some fonctionnality of windows need this service. Maybe you don't use them. So, to simplify the administration, I prefere have the same configuration on all servers and keep windows time service. But if you want to use VMWare Tools, you can disable the windows time service.

Olivier

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We have all our ESX hosts synching to our NTP server and all VMs synch to the ESX host and the windows time service is disabled. Been running that way for over 2 years without any issues.

The problem with leaving both running is that they are not aware of each other and both can move the time on the VMs. Check out Timekeeping inf Virtual Machines for an in-depth discussion of the way it works.

If your servers are part of an AD domain then they should have Windows Time Service enabled and VMware Tools Time Sync disabled. The exception to this being your PDC emulator which is at the top of the AD time pyramid. Your PDC emulator needs Windows Time Service enabled and VMware Tools Time Sync enabled to sync NTP time with the ESX server. Accurate timekeeping is critical to the proper operation of Kerberos and your member servers should only sync from one source (WTS). More on this below...

Configuring windows time service (not in ESX) - http://www.windowsnetworking.com/articles_tutorials/Configuring-Windows-Time-Service.html
Vmware time sync and windows time service (understand windows time first) - http://kb.vmware.com/kb/1318
Time sync - http://www.vmware.com/community/thread.jspa?forumID=21&threadID=16115&messageID=186017
Timekeeping in VMware virtual machines - http://www.vmware.com/pdf/vmware_timekeeping.pdf
How to configure an authoritative time server in Windows Server 2003 - http://support.microsoft.com/kb/816042
Virutalization of Active Directory - http://www.vmware.com/community/thread.jspa?messageID=352424
Considerations when hosting Active Directory domain controller in virtual hosting environments - http://support.microsoft.com/kb/888794
Virtualizing a Windows Active Directory Domain Infrastructure - http://download3.vmware.com/vmworld/2006/tac9710.pdf

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Thanks, Eric
Visit my website: http://vmware-land.com
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Hi,

Can I clarify this, as in our environment I have Virtualised our PDC emulator and used the Vmtools time sync option etc this is all working fine its our member servers that we have trouble with. They are still relying on w32 time service under windows the problem we get on the member servers is the time drift associated with not having a hardware clock, my only solution that I could come up with was to setup a scheduled task to run a timesynce at certain periods during a day to keep the guests clock in sync.

The last reply sort of contradicts my findings in our environment, again I repeat the Domain controllers are not a problem and have configured them as per Vmware recommendations and the MS guides, it is only the member servers.

My way of thinking is I have a fix with a scheduled task or I disable w32time service under windows and just use the VMware tools option for time sync.

regards

Mark

I'd stick with Windows Time Service on the member servers...just double check they are using the PDC Emulator by

net time /querysntp - should say perversely --- 'no time server configured for this host'

If it says anything else use..

net time /setsntp

You can always trying reducing the time period between sync's

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Parameters

DWORD Period = 65532

This will give you a SYNC once every 45 minutes until 3 good synchronizations occur, then once every 8 hours (3 per day)

http://support.microsoft.com/kb/223184

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Windows Time in Guest OS

Windows Time in Guest OS