Today I learned some interesting yet simple detail about time sources and the Windows Time Service . After noticing that one of two Domain controllers in a little Development/Test domain we have was about 6 minutes out of sync I learned from a college of mine the best and quickest way to query the time sources and change it if needed.
In the Registry sub Key: HKLM\Machine\System\CurrentControlSet\services\W32Time\Parameters there is a string called Type that can have the value of NT5DS or NTP.
NT5DS means the computer is part of a domain syncs its clock with the Domain controller that is the role holder of the PDC FSMO role, while NTP means the server syncs its time with an specified time source. The NTP source is in a value within the same sub key called NtpServer. Clients that sync with a PDC can still have a value in the NtpServer string but the PDC emulator will be the one they sync with if the Type is set to NT5DS.
In my scenario with the Domain controller that was out of sync, it had been configured to sync with and external time source but being on a segregated network with no internet access, after a few years the time on the server had drifted.
Another interesting topic around time sync is the option for VMware Virtual Machines to synchronise guest time with host. I can see this put to use on Stand-Alone servers that need to be on a segmented network such a CDE network with no access to a NTP Server. One point to mention though is that regardless of this option being used or not on the Virtual Machine, VMTools will sync the OS with the host clock when doing certain operations such as reverting a snapshot, power on and restart (via VMTools) so it is always important that your ESXi hosts have their NTP configurations correctly configured..