We have some windows server 2008 VMware instances on multiple physical servers (hosted) and an application which requires the time to be synced across the server instances.

Obviously, VMware has problems with this and we really have never gotten it working any better, we have setup the servers to poll for an NTP update every minute which mitigates the problem (in a fairly crude way). Except that every once in a while, the update will fail (because there's already too much drift) and then windows never does an NTP update afterwards which eventually allows the servers to drift far enough apart that our application breaks, and we notice.

We are thinking about changing hosts to Xen servers on approximately the same setup, and I anticipate similar problems.

1. can anyone tell me if Xen has the same time-drift issues VMware does, for guests?
2. can anyone tell me what the best windows server settings are for syncing with an external NTP server to keep things in sync:
   1. how frequently do you recommend syncing? (assuming every minute)
   2. do you recommend running our own NTP server - even if it has to be on a virtual instance? (assuming not)
   3. is there any way to tell windows to sync with the NTP server no matter what the time difference is?
   4. any other suggestions for keeping windows servers time in sync?

I have become familiar with [ http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1318 ] and it's helped, but it's not been totally effective (see above).

thanks much!