I'm trying to decide the best way to configure time synchronization for our Server 2003 VMs. In our environment most of the Windows servers are physical, but we are slowly migrating to VMs. All Windows servers are joined to a domain, and thus get their time sync'd using the Windows time hierarchy. We have configured our ESXi 4.0 hosts with a NTP server, which is the same time source our Windows PDC emulator uses.
Now my question is, should we totally disable VMware time sync (using the six VMX configuration tweaks) and totally rely on w32time, or disable w32time and rely on VMware tools time sync? My first inclination is to disable VMware time syncing and rely on w32time so all Windows servers are using the same source.
According to the VMware time sync guide for 3.x "At this writing we do not yet have specific recommendations on how to configure W32Time for best
performance in a virtual machine." Some blogs favor disabling all VMware time sync, and yet VMware seems to recommend using VMware tools.
I don't want BOTH going on, as there may be some time deltas between ESX hosts and the Windows SNTP time. What do enterprises typically do? I'm a pretty firm believer in minimizing the number of time sources, so that leads me down the path of disabling VMware time sync and rely on w32time.
In the vSphere performance best practices I found:
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For the most accurate timekeeping, consider configuring your guest operating system to use NTP, Windows Time Service, or another timekeeping utility suitable for your operating system. The time-synchronization option in VMware Tools can be used instead, but it is not designed for the same
level of accuracy as these other tools and does not adjust the guest time when it is ahead of the host time. We recommend, however, that within any particular virtual machine you use either the VMware Tools time-synchronization option, or another timekeeping utility, but not both
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So that seems to boost my thoughts of disabling VMware time sync, and relying on W32time.