VM Time Sync 1 millisecond accuracy

Question

I have setup my virtual machines to sync with the host. So if I run w32tm /query /status, then I see Source: VM IC Time Synchronization Provider.

However, the pollinterval (the frequency with which it syncs to the host) is 10 seconds; in reality, it only does it every 16 seconds.

I need 1 millisecond time accuracy for my needs, which Microsoft offers, provided I am sub Stratum 5 (which I am, at 4).

However, to get this 1 millisecond time accuracy, I need to increase the frequency with which the machine syncs. How can I do that? The Azure machine seems to only sync every 16 seconds no matter what I change the pollinterval to.

For reference, here is the article from Microsoft explaining 1ms accuracy: https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/support-boundary

Answer 1

A machines time is only as good as the source clock it synchronizes with. In order to achieve 1 ms of accuracy, you'll need GPS hardware or a time appliance on your network you reference as the master source clock. Using the default of time.windows.com, may not provide a stable and local time source. Additionally, as you get further away from the source clock, the network affects the accuracy. Having a master source clock in each data center is required for the best accuracy.
https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/windows-server-2016-improvements#solid-source-clock

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Answer 2

The post regarding 1ms accuracy is actually for azure. That is indeed the only thing capable of the accuracy without its own GPS; the instructions are for syncing to the host (for virtual machines). Yet, the 16 second updates seem to make this not possible despite what's stated in those articles.

Answer 3

Thanks, I've read through this and have configured with the limited information that is contained in those links. I actually posted the link you're referencing, noting that I am not achieving 1ms accuracy despite following configuration. I suspect that the issue is the pollinterval to sync with the host is 16 seconds. It should be more frequent than that to ensure 1ms accuracy; however, the virtual machines are not permitted to sync more frequently. So has anyone actually achieved 1ms accuracy with this configuration? Cause it doesn't seem possible given the 16 seconds.

Answer 4

1 ms = 10,000 clock ticks. More requirements mentioned here.
https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/support-boundary?source=recommendations#target-accuracy-1-millisecond

and more here on configuration.
https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/configuring-systems-for-high-accuracy
https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/windows-time-service-tools-and-settings

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Answer 5

Read on here about time sync configuration in Azure.
https://learn.microsoft.com/en-us/azure/virtual-machines/windows/time-sync
https://learn.microsoft.com/en-us/windows-server/networking/windows-time-service/configuring-systems-for-high-accuracy

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