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Time Sync with HyperV


I had a client recently who dropped in a 2012 datacenter HyperV host alongside their VMware host and they had a small issue of network drives disconnecting periodically coinciding with some errors in the logs regarding time sync. In this case they had new DCs setup on the new HyperV but the FSMO roles were still with the old DCs (2008r2 on VMware) temporarily with the old PDC using an external Time source.

At this juncture it was worthwhile to look at how Time was working in the entire environment. Some new (Server 2012) info came to light so I thought I would provide some valuable commands and links to resources which can help you sort out Time sync errors or weirdness before it becomes a major problem.

First of all it’s valuable to know where your Time is coming from:
Open up a CMD window and run “netdom query fsmo“. That tells you which server is your primary domain controller (the server which should be your Time provider). All your other DCs, servers and workstations should be getting their Time from this server, but not by referencing it directly; they go through the Active Directory structure. More on that in a bit.

Where is this server/workstation getting its Time from?:
Open up a CMD window and run “w32tm /query /status” and you’ll see where it is pointed.

This server/workstation isn’t getting Time from the server I was expecting…:
If this is a workstation getting Time from a secondary DC that’s OK. All this means is that the machine authenticated with that particular DC. If the source is anything other than a DC or if the computer you’re on is a DC (not the PDC) and it’s not pointing to the PDC then it could be a problem.
2012 HyperV Guest VM note: If your time provider shows up as “VM IC Time Synchronization Provider” then that machine is configured to point to the HyperV host for Time sync.

I think I should reset the Time service:
This can be very helpful when troubleshooting. Open up a CMD window on the computer you want to reset and run these commands:

net stop w32time
w32tm /unregister
w32tm /register
net start w32time

w32tm /resync

w32tm /query /status

2012 HyperV Guest VM note: This should reset the VM to use domain time or a remote time server (depending on your setup) instead of the HyperV Host VM IC Time.


Note about VM IC Time Synchronization:
Never disable the Host VM IC Time…it’s needed for many different host operations.

Special consideration for Virtualized Environments:
Virtualized domain controllers and virtualized machines in general tend to lose time much faster than a physical computer. For this reason the Time providing PDC should be configured to check its external time source frequently. MS recommends once every 15 minutes as a good starting point.



This site has some great info on Time. Unlike my post, it goes in depth to provide a complete understanding of how you can get Time setup.

This post has all the info you ever wanted to know about HyperV and Time Sync along with some Q/A for different network configurations which you may find very useful.

This one was a recommendation from a post on Experts Exchange…I didn’t review this post so YMMV using it to solve your problems.


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