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I have 27 2008R2 servers (all Hyper-V guests) that recently started running fast. There are other 2008R2 servers on the same hosts that run spot on. The time averages from 2 to 3 minutes fast but at times has gotten to as much as 20 minutes. If I run w32tm /striptchart against the master clock server I can see the time change very quickly, as much a second faster every second. It varies sometimes it is slower. I can run w32tm /resync and see the time go back to correct but it quickly starts to drift again. I do not think it is a sync issue but rather the clock actually running fast. Thank you for any help.

Mark

  • Does the time on the Hyper-V host run fast as well? What hardware is your Hyper-V hosts running on? – Nixphoe Oct 25 '18 at 19:35
  • No all of the host servers are keeping good time. They are mixture of HP Proliant and Dell PowerEdge servers. – Mark Oct 25 '18 at 19:37
  • Are these VM's joined to an AD domain? – joeqwerty Oct 25 '18 at 20:35
  • Yes they are all members of the domain. – Mark Oct 25 '18 at 22:51
  • What is the 'master clock server' and what is it synchronizing with? – Greg Askew Oct 27 '18 at 16:04
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On a virtual machine all of the "hardware" is abstracted and running in software, generally speaking. The part of the system that keeps time is running in software on the CPU of the host. Depending on physical CPU load and likely clock frequency of the physical CPU the time calculation is going to drift. Hyper-V includes a time synchronization service (advanced -> integration services) that takes the time from the host, which keeps its time via dedicated hardware clock, and forces the guests to update their clocks if you have that turned on.

I have personally seen hosts and guests drift because of virtual Domain Controllers. The host asks the domain for time and the guest DC has drifted a bit and replies with the wrong time. The host then changes the time on all guests. That loop continues in small increments until there is very noticeable drift and possibly enough for Active Directory functions to start failing if you don't notice it in time.

To solve my Host/Guest drift issues I use a simple little time update program on all my Hyper-V hosts that syncs with the forest PDC Emulator that is on a physical box.

  • 3 of the 27 servers that are having issues are domain controllers that have been serving the time precisely for several years. I am working on replacing them since the time being off is causing other issues. The PDC is also a VM and is still keeping good time. – Mark Oct 25 '18 at 23:01

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