Time Synchronization in Hyper-V

There is a lot of confusion about how time synchronization works in Hyper-V – so I wanted to take the time to sit down and write up all the details. 

There are actually multiple problems that exist around keeping time inside of virtual machines – and Hyper-V tackles these problems in different ways.

Problem #1 – Running virtual machines lose track of time.

While all computers contain a hardware clock (called the RTC – or real-time clock) most operating systems do not rely on this clock.  Instead they read the time from this clock once (when they boot) and then they use their own internal routines to calculate how much time has passed.

The problem is that these internal routines make assumptions about how the underlying hardware behaves (how frequently interrupts are delivered, etc…) and these assumptions do not account for the fact that things are different inside a virtual machine.  The fact that multiple virtual machines need to be scheduled to run on the same physical hardware invariably results in minor differences in these underlying systems.  The net result of this is that time appears to drift inside of virtual machines.

UPDATE 11/22: One thing that you should be aware of here: the rate at which the time in a virtual machine drifts is affected by the total system load of the Hyper-V server.  More virtual machines doing more stuff means time drifts faster.

In order to deal with time drift in a virtual machine – you need to have some process that regularly gets the real time from a trusted source and updates the time in a virtual machine.

Hyper-V provides the time synchronization integration services to do this for you.  The way it does this is by getting time readings from the management operating system and sending them over to the guest operating system.  Once inside the guest operating system – these time readings are then delivered to the Windows time keeping infrastructure in the form of an Windows time provider (you can read more about this here: https://msdn.microsoft.com/en-us/library/bb608215.aspx).   These time samples are correctly adjusted for any time zone difference between the management operating system and the guest operating system.

Problem #2 – Saved virtual machines / snapshots have the wrong time when they are restored.

When we restore a virtual machines from a saved state or from a snapshot we put back together the memory and run state of the guest operating system to exactly match what it was when the saved state / snapshot was taken.  This includes the time calculated by the guest operating system.  So if the snapshot was taken one month ago – the time and date will report that it is still one month ago.

Interestingly enough, at this point in time we will be reporting the correct (with some caveats) time in the systems RTC.  But unfortunately the guest operating system has no idea that anything significant has happened – so it does not know to go and check the RTC and instead continues with its own internally calculated time.

To deal with this the Hyper-V time synchronization integration service detects whenever it has come back from a saved state or snapshot, and corrects the time.  It does this by issuing a time change request through the normal user mode interfaces provided by Windows.  The effect of this is that it looks just like the user sat down and changed the time manually.  This method also correctly adjusts for time zone differences between the management operating system and the guest operating system.

Problem #3 – There is no correct “RTC value” when a virtual machine is started

As I have mentioned – physical computers have a RTC that operating systems look at when they first boot to get the time.  This real-time clock is backed by a small battery (you have probably seen the battery yourself if you have ever pulled apart a computer).  Unfortunately virtual machines do not have any “batteries”.  When a virtual machine is turned off there is no component that keeps track of time for it.  Instead – whenever you start a virtual machine we take the time from the management operating system and put this into the real-time clock of the virtual machine.

This is done without the use of the Hyper-V time synchronization integration servers (it happens long before the integration services have loaded). 

The downside of this approach is that this does not take into account any potential time zone differences between the management operating system and the guest operating system.  The reason for this is that “time zones” are a construct of the software that runs in a virtual machine – and is not communicated to the virtual hardware in any way.  So – in short – when we start a virtual machine there is no way for us to know what time zone the guest operating system believes it is in.

One partial mitigation we have for this issue is that when the Hyper-V time synchronization component loads for the first time – it does an initial user mode set of the time to ensure that the time gets corrected as quickly as possible (using the same technique as discussed in problem #2).

…

So now that you understand how this all works – let’s discuss some common issues and questions around virtual machines and time synchronization.

Question #1 – I have a virtual machine that is configured for a different time zone to the management operating system. Should I disable the time synchronization component of Hyper-V?

No, no, no, no, no, no, no.  And I say again – no.  As I have mentioned above – all time synchronization that is done by the Hyper-V time synchronization integration service is time zone aware.  If you disable the Hyper-V time synchronization integration service you will disable all the time synchronization aspects of Hyper-V that are time zone aware – and only leave the initial RTC synchronization active – which is not time zone aware.

This means that your virtual machines will go from booting in the wrong time zone, and then being corrected as soon as the Hyper-V time synchronization integration service loads to booting in the wrong time zone and staying in the wrong time zone.

Question #2 – Is there any way that I can stop Hyper-V from putting the wrong time in the RTC at boot?

In short; no.  We need to put something in there – and that is the best thing that we have to work with.

Question #3 – Can’t you use UTC time in the RTC so that the correct time is established when the virtual machine boots?

UTC (which is the computer techy version of saying GMT) time would solve this problem nicely with only one problem.  Windows does not support UTC time in the BIOS (Linux does).  So while this would solve the problem for our Linux running user base – the fact of the matter is that most of our users run Windows – and this would not work for them.

Question #4 – What about if I am using a different time synchronization source (e.g. domain time or a remote time server)?

Hyper-V time synchronization was designed to “get along well” with other time synchronization sources.  You should not need to disable Hyper-V time synchronization in order to use a different time synchronization source – as long as it goes through the Windows time synchronization infrastructure.

In fact – if you are running a Domain Controller inside a virtual machine I would recommend that you leave Hyper-V time synchronization enabled but that you also setup an external time source.  You can do this by going to this KB article: https://support.microsoft.com/kb/816042 and following the steps outlined in the “Configuring the Windows Time service to use an external time source” section.

UPDATE 11/22: I should have mentioned: since virtual machines tend to lose time much faster than physical computer, you need to configure any external time source to be checked frequently.  Once every 15 minutes is a good place to start.

Question #5 – How can I check what time source is being used by Windows inside of a virtual machine?

This is easy to do.  Just open an administrative command prompt and run “w32tm /query /source”.  If you are synchronizing with a remote computer – its name should be listed.  If you are using the Hyper-V time synchronization integration service you should see the following output:

If you see this output:

It means that there is no time synchronization going on for this virtual machine.  This is a very bad thing – as time will drift inside of the virtual machine.

Question #6 – Wait a minute! My virtual machine should be synchronizing to the domain (or an external server) – but when I run that command it tells me that the Hyper-V time synchronization provider is being used! How do I fix this!

I do not know why this happens – but sometimes it happens.  The first thing that you should do is to check that your domain does have a correctly configured authoritative time source.  There have been a small number of times when I have seen this problem being caused by the lack of an authoritative time source.

Alternatively – you can “partially disable” Hyper-V time synchronization.  The reason why I say “partially disable” is that you do not want to turn off the aspects of Hyper-V time synchronization that fix the time after a virtual machine has booted for the first time, or after the virtual machine comes back from a saved state.  No other time synchronization source can address these scenarios elegantly.

Luckily – there is a way to leave this functionality intact but still ensure that the day to day time synchronization is conducted by an external time source.  The key thing trick here is that it is possible to disable the Hyper-V time synchronization provider in the Windows time synchronization infrastructure – while still leaving the service running and enabled under Hyper-V.

To do this you will need to log into the virtual machine, open an administrative command prompt and run the following commands:

reg add HKLM\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\VMICTimeProvider /v Enabled /t reg_dword /d 0

This command stops W32Time from using the Hyper-V time synchronization integration service for moment-to-moment synchronization.  Remember from earlier in this post that we do not go through the Windows time synchronization infrastructure to correct the time in the event of virtual machine boot / restore from saved state or snapshot.  So those operations are unaffected.

w32tm /config /syncfromflags:DOMHIER /update

This command tells Windows to go and look for the best time source in the domain hierarchy.  If you want to use an external time server instead you can use the commands found here: https://technet.microsoft.com/en-us/library/cc784553(WS.10).aspx

net stop w32time & net start w32time

w32tm /resync /force

These two commands just “kick the Windows time service” to make sure the settings changes take effect immediately.

w32tm /query /source

This final command should confirm that everything is working as expected.

When you run these commands you should see something like this:

Question #7 – I have a virtual machine that has gotten ahead of time, and it never gets corrected back to the correct time. What is going on here?

As a general rule of thumb, when time drifts inside a virtual machine it runs slower than in the real world, and the time falls behind.  We will always detect and correct this.

However, in the past, we have had reports of software problems caused when the Hyper-V time synchronization integration service decides to adjust the time back – because it believes the virtual machine is ahead of time.  To deal with this (rare) issue – we put logic in our integration service that will not change the time if the virtual machine is more than 5 seconds ahead of the physical computer.

UPDATE 11/22: I was asked how having the virtual machine in a different time zone to the Hyper-V server would affect this.  The short answer is that it does not.  The 5 second check is done after we have done the necessary time zone translation.

Question #8 – When should I disable the Hyper-V time synchronization service (either in the virtual machine settings, or inside the guest operating system)?

Never.

There are definitely times when you will want to augment the functionality of the Hyper-V time integration services with a remote time source (be it a domain source or an external time server) but the only way to get the best experience around virtual machine boot / restore operations is to leave the Hyper-V time integration services enabled.

Hopefully you will all find this information useful

Cheers,
Ben

Comments

• Anonymous
  November 19, 2010
  Dave Atkinson - You had some good questions - which I will be happy to answer if you can post them without linking to the site that advertises your software.  Sorry about deleting your comment - but I get a lot of spam attempts here and have a strict policy against any form of advertising in comments. Cheers, Ben

• Anonymous
  November 19, 2010
  Sorry about that I do it from habit  :-) I love your article and I had a few questions. I just finished a P2V of my SBS 2003 DC and I was having a big problem with time drift. I tried turning off C2 states in the host BIOS, did all kinds of messing around with w32time and registry settings, and nothing was working. Time on my DC would drift considerably, affecting every machine on the network. If you have other VMs on the same machine that are Domain members, what is the best practice? If you "partially disabled" integration svcs time sync as in #6 above, and still had those machines point to the PDC emulator (in my case a single virtual DC), would you have to lower the time sync period so that it closely matches what integration svcs does? I can bring up the clock on these machines and watch the second hand stop for several seconds at a time - they start to drift very quickly. What time sync interval is safe for things like source control, Kerberos auth, etc.? I want to be sure when I check in my files and perform other Source Control-type operations that time stamps are all good and things make sense. Alternately, should you sync the host to an external time source and allow integration svcs time sync on all your VMs, ignoring Domain hierarchy altogether? Thanks for the great article, Dave

• Anonymous
  November 20, 2010
  For question 7, does it mean if the VM is running ahead of the physical machine, we will not correct it by Hyper-V time synchronization service? So we have to configure a remote time source to correct it somehow?

• Anonymous
  November 20, 2010
  with regards to the timezone of the clock, couldn't that be part of the VM's metadata? what timezone the clock should be on startup/restore? (and whether it should be adjusted for daylight savings)

• Anonymous
  November 21, 2010
  Hi Ben I see alot of confusion over this particular subject, but I have seen a microsoft article about domain controllers as VM guests and they advise to disable the Time Sync service. Quoted here: "For virtual machines that are configured as domain controllers, disable time synchronization with the host through Integration Services. Instead, accept the default Windows Time service (W32time) domain hierarchy time synchronization. Host time synchronization makes it possible for guest operating systems to synchronize their system clocks with the system clock of the host operating system. Because domain controllers have their own time synchronization mechanism, host time synchronization must be disabled on virtual machines that are configured as domain controllers. If domain controllers synchronize time from their own source and also synchronize time from the host, the domain controller time can change frequently. Because many domain controller tasks are tied to the system time, a jump in the system time could cause lingering objects to be left in the directory and replication to be stopped. " Reference: technet.microsoft.com/.../dd348449%28WS.10%29.aspx I want to follow best practice but it seems there is soo much conflicting advice out there. kind regards Zoel

• Anonymous
  November 21, 2010
  The comment has been removed

• Anonymous
  November 21, 2010
  The comment has been removed

• Anonymous
  November 22, 2010
  The comment has been removed

• Anonymous
  November 22, 2010
  The comment has been removed

• Anonymous
  November 22, 2010
  The comment has been removed

• Anonymous
  November 26, 2010
  Hi Ben, I have another unralated question about the Topic but related to Hyper-V When i started virtualizing i didnt pay much attention to which disk, was which clustered disk. And now i have a huge mess. I need to expand some disk but im not quite sure which is which. For Example: Disk 1- Clustered Disk 10 - Volume3 Is there anyway to mix and match what Clustered disk is what "phisical" LUN?

• Anonymous
  November 29, 2010
  Just a quick note on this, we had a dev server which was scheduled for a nightly reboot @ 12.30 am.  When daylight saving kicked in, it started rebooting continually for an hour from 12.30 to 1.30, as the task scheduler would start, (and the system time would be, eg, 11.35), THEN the time sync service woulds start, adjust the time from 11.35 to 12.35, then the task scheduler would see this change, and trigger all events due between 11.35 and 12.35, so the reboot got requeued, etc.  To make matters even more fun, there were tasks queued at 1 am, and these were also starting and stopping for half an hour as the system did it's nightly hour long death spiral.  To fix this, we changed the scheduler service so it was dependant on the time sync service. (KB 193888) It's probably worth noting that scheduled reboots will be affected by this time zone change, unless the scheduler is started after the time sync service.

• Anonymous
  November 29, 2010
  Just a quick note on this, we had a dev server which was scheduled for a nightly reboot @ 12.30 am.  When daylight saving kicked in, it started rebooting continually for an hour from 12.30 to 1.30, as the task scheduler would start, (and the system time would be, eg, 11.35), THEN the time sync service woulds start, adjust the time from 11.35 to 12.35, then the task scheduler would see this change, and trigger all events due between 11.35 and 12.35, so the reboot got requeued, etc.  To make matters even more fun, there were tasks queued at 1 am, and these were also starting and stopping for half an hour as the system did it's nightly hour long death spiral.  To fix this, we changed the scheduler service so it was dependant on the time sync service. (KB 193888) It's probably worth noting that scheduled reboots will be affected by this time zone change, unless the scheduler is started after the time sync service.

• Anonymous
  December 06, 2010
  I also vaguely remember certain VMs of mine (Windows Server 2003 I think) moaning with time related warnings and errors in the event log.  Disabling Time Synchronization for the guests stopped these from appearing.  BTW, the guests in question were domain members getting their time from local DCs so disabling the synchronization wasn't an issue. Just found a link which described my issue; www.mcbsys.com/.../w32time-errors-in-a-hyper-v-virtual-environment

• Anonymous
  December 06, 2010
  I'm dealing with this issue for quite some time now in an enterprise environment and for sure i can tell, that the problem is solved for Windows Server 2003 VMs by reinstalling the HyperV Guest Services and disabling the HyperV Time Service. For 2008 R2 servers, however, this "trick" doesn't work as the services are more integrated into the core system. Overall i tried almost everything i could find in the internet and still searching for a solution for 2k8r2-servers. Even if there is the dc listed after the "w32tm /query /source" command the next day you just have more Event50 in the log. I also tried manipulating registry values like "SpecialPollInterval" but no effect. My last hope right now is "question 6" from this article. @Virtual PC Guy: Any Update regarding the Services-matter (keep them on or off)? My best guess right now is that if the host is really on its limit that it doesn't matter what you do - the warning will happen. Thats not a good sight, however.

• Anonymous
  February 20, 2011
  [Disclaimer: I am working for a hardware vendor selling computer clocks, e.g. for PCI / PCIe bus] I wonder why Hypervisors do not include the possibility to allow their VMs to access a hardware time source during runtime. The RTC is one choice, but since it only has a 1s resolution it could probably only be a last resort time source. Using a dedicated hardware clock [see disclaimer], offered by some vendors, and allowing VMs to access this device either directly or indirectly would resolve a lot of timing related issues that our customers report to us. Maybe redirecting the system calls to read the current time to a function that reads the hardware clock would already help, or integrating this possibility into the Hypervisor-specific utilities running inside the VMs (like the Hyper-V time sync service). Regarding the UTC/Localtime problem with the RTC: Why don't you allow people to specify in which time zone the RTC for a specific VM is operating? That way you could set the initial time correctly for each VM. Regards,  Heiko

• Anonymous
  May 11, 2011
  The comment has been removed

• Anonymous
  May 15, 2011
  Have you any thoughts on what to do about the time source for a Domain Controller on an "Internal only" virtual network?  I can't sync to an external time source because there isn't one on the internal network.  I've tried turning off w32time sync'ing by setting HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParametersType to NoSync but after a bit of indecision, it tells me Event ID 144: "The time service has stopped advertising as a good time source."

• Anonymous
  June 29, 2011
  I can confirm the post of Ryan P. I have a Server 2008 R2 as Hyper-V host running a Server 2008R2 guest. Only disabling the time sync in the integration services stops the guest from sync-ing time with the host. Setting the VMICTimeProviderEnabled to '0' doesn't seem to work (not even after a reboot of the guest). I saw the guest concerned sync-ing time with an external source every 80 seconds, only to be "corrected" back by the host. Maybe something changed in R2?

• Anonymous
  June 29, 2011
  Correction to my previous post (Jun 30 11:15): Setting the "Enabled" registry value to 0 seems to work as explained for servers that are not time servers themselves (i.e. in my case Domain Controllers). It definitely doesn't work on servers that are supposed to sync with an external clock and that function as time servers themselves.

• Anonymous
  October 31, 2011
  If we had a virtual server as a domain controller and we were to have small application running to sync to the time in the virtual server would we see something like the whole system cripping forward in time like 7 minutes over 2 weeks?

• Anonymous
  May 01, 2012
  Hi Ben! Is there a way to disable time sync for a single machine and set the timer of this machine to a special date / time? I need to run an old server image and set it's time to 2009. Thank you! Regards Ingo

• Anonymous
  May 10, 2012
  It seems to me that there are mixed messages from microsoft on this topic which is never good, as that tends to mean that the best solution depends on your environment. However if you read various MS and MVP articles you will certainly be thinking what is the correct answer support.microsoft.com/.../976924 , blogs.msdn.com/.../time-synchronization-and-domain-controller-vm-s.aspx etc etc So what is the current recommendation from Microsoft on this topic ? Can we have an update as I have found mixed success using Integration Services and External time sources, in fact at one site we had MS Support connected in for three days trying to get it to work.

• Anonymous
  July 11, 2012
  The comment has been removed

• Anonymous
  July 25, 2012
  What do you reccommend as the best way to configure a Linux VM on hyperv so that they time is in sync and correct. Our Linux VM time advances over time. We are a microsoft shop so we use hyperv however there are instances where we need to use a linux vm Any suggestions you have would be greatly appreciated. Thanks in advance

• Anonymous
  July 29, 2012
  Hi Ben - reg key fix doesnt work. Instructions followed exactly. I've configured my time source externally to a list of pool.ntp.org servers. When using /resync /force it sets the time correctly, but then about a second later the host machine overwrites it. Hopefully I can find a fix as I dont want to disable the integration service, but looking like thats the only way to get this going.

• Anonymous
  August 08, 2012
  Thank you for your article... We are getting constant barrage of system event logs about every 30 seconds that the time has been updated in our VMs .... Am I correct to assume that this is normal? Thanks!

• Anonymous
  December 03, 2012
  Does Hyper V 2012 resolve the time issues? Specifically, using a virtual domain controller (windows 2008r2) on Hyper V we have had to disable Hyper V time synchronization services and resort to third party time keeping software. We were consistently dealing with wide variations in time and resulting in security policy failures and etc. We have a Hyper V host that gets time from an ntp server and the PDC does as well. Disabled HyperV time sync and installed third party time keeper on all hosts and VMs.

• Anonymous
  December 17, 2012
  Ben, the Microsoft recommendation for time keeping of DC's on Hyper-V seems to be changed again? technet.microsoft.com/.../virtual_active_directory_domain_controller_virtualization_hyperv(WS.10).aspx updated October 24, 2012: Note: This guidance has been recently updated to reflect the current recommendation to synchronize time for the guest domain controller from only the domain hierarchy, rather than the previous recommendation to partially disable time synchronization between the host system and guest domain controller. There was always a lot of discussion around time keeping of DC's on Hyper-V and partially disabling time services seemed to be the solution, but now again several articles conflict with each other.

• Anonymous
  March 18, 2013
  Hi Ben, great article, still proving useful over 2 years on! We have just moved 2 DCs to HyperV VMs and your Question 6 helped fix the issue we were experiencing but I have a question about the update you added "UPDATE 11/22: I should have mentioned: since virtual machines tend to lose time much faster than physical computer, you need to configure any external time source to be checked frequently.  Once every 15 minutes is a good place to start." Our PDC Emulator is still a physical server that checks with an external NTP source. Does that update just apply to clients with external sources configured or Domain clients too? Do you mean I should change the frequency on all VMs, or just virtual DCs, or just the PDC emulator? If so, how exactly do I check the existing frequency and how do I modify it? Many thanks @thommck

• Anonymous
  July 15, 2013
  And how would you go about setting the date time to something in the past, because we need to test certain functionalities? At the moment in our virtual machine running XP we cannot set the date to something in the past, as it just resets itself within a few seconds, but it has no problem if we set the date to something in the (far) future..

• Anonymous
  August 07, 2013
  Hi Ben, great post. Three years on do Microsoft not have a fix for this issue? Surely you should be able to sync all your hyper-V hosts to a reliable time source then rely on integration services?

• Anonymous
  October 30, 2013
  I am always sad when I see contradictory information... I know changes happen, people misunderstand, mis-communicate...  But I am inclined to believe that this blog post above, despite it's age is correct and the one from this year is incorrect.  Please set us straight Ben!  And then request an edit to the one below.  I tried to add community contributions to the article below, but it failed with no explanation. technet.microsoft.com/.../dd363553(WS.10).aspx

• Anonymous
  December 09, 2013
  What happens if the w32time service isn't running (e.g. because it is for triggered start when the machine joins a domain)? Does Hyper-V still try to discipline the clock from the host (if so how and when) or does no correction take place?

• Anonymous
  December 09, 2013
  (following on from previous) Would a way round this be to delete the triggers on the w32time service and set its startup type to automatic (social.technet.microsoft.com/.../windows-time-startsstops-at-system-startup ) ?

• Anonymous
  April 01, 2014
  The recommendation to not disable time sync made in the article is being quoted in Technet - as well as other Microsoft sources that directly contradict this advice. social.technet.microsoft.com/.../20-minute-time-drift-on-ws2012-virtual-dc

According to this source: "This guidance has been recently updated to reflect the current recommendation to synchronize time for the guest domain controller from only the domain hierarchy, rather than the previous recommendation to partially disable time synchronization between the host system and guest domain controller." technet.microsoft.com/.../dd363553(WS.10).aspx * The email discussion with the other team was taking place in 2010. It's 2014. What was the conclusion? What do we tell the customer?

• Anonymous
  May 22, 2014
  Question #6 - how can i back to hyper-v time synchronization?

• Anonymous
  May 30, 2014
  The comment has been removed

• Anonymous
  June 12, 2014
  Very nice and interesting article. Thxs a lot. We can complete with this link : serverfault.com/.../hyper-v-time-sync-for-vm-domain-controller Cheers, Yvan

• Anonymous
  July 20, 2014
  Thanks for the explanations and the Windows time provider. But actually my guest is Linux (Ubuntu 13.10 server), how do I fix it there. It is quite important because I just found out that my VM produces wrong timestamp on different remote systems, e. g. in the source code repositories as well as systems depending on correct timestamps. Cheers Marco

• Anonymous
  August 04, 2014
  The time drift is causing SCCM PXE boot to fail to retrieve policies, preventing OS deployment.  How can I correct the time on a VM that doesn't have an OS installed yet?

• Anonymous
  September 29, 2014
  The comment has been removed

• Anonymous
  October 01, 2014
  I just installed Hyper-V today, and to be honest it's my first time ever using any kind of VM. But I've been sitting here reading info and playing around for hours and am quickly learning a lot of stuff. I set it up several hours ago because of the Windows 10 Preview; anyway noticed that my clock was way off, came across this thread and after looking into it - I noticed something really funny. It turned out all that was wrong was that the time zone of the clock in the VM was incorrect LOL. Just thought I'd mention it because I'm sure that I'm not the only one that has overlooked this :P

• Anonymous
  December 15, 2014
  The comment has been removed

• Anonymous
  February 22, 2015
  This is typical for Microsoft - nobody really knows what is actually the correct way of doing things. It is ridiculous to get contradictory information for such important topics.

• Anonymous
  December 06, 2015
  Hi Ben, On question number 5: I see Local CMOS clock and this is my PDC, how can I change it? Thanks!

• Anonymous
  January 11, 2016
  The comment has been removed

  • Anonymous
    February 02, 2016
    We have configured our DCs like Ben suggests, but it appears that disabling VMIC time provider does not work. The time on a DC is changing to the time of the host anyway. We're gonna open a case to MS on this problem.

• Anonymous
  January 19, 2016
  Thanks for the information, Ben. I had PDC Guest VM that has wrong time. These are all 2012 DataCenter. I started noticing this problem when I enable auto update on the host that has the PDC VM in it. I guess when it restarts, it has chicken and egg problem when it comes to whose time to use. What I ended up doing is:

1. Set the host OSes to sync up with external source.
2. For the PDC and additional DC's that are VM's, I set it to sync up with external source, but VMIC timer registry to 0.
3. For all other non domain controller VM's, no mods to the registry key, and kept the Hyper-V time sync checked.

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  April 12, 2017
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