Changing NTP Settings

[cglavish]

Good day,

We have noticed that we have time discrepancies between our virtualized servers and our physical servers.  The difference is about 5 minutes.

Our internal time server (Netware 6.5 sp5), which uses the external sources of 129.7.1.66/207.123.2.72/192.5.41.41 is 5 minutes behind the time that is on our VM's.

The VM's are getting their time from the Esxi 4.1 host, via vmtools.  The Esxi host is using NTP and is pointing to 192.5.41.41.  I have also noticed that on some of the Windows Server VM's, in the windows o/s ntp is also configured (thinking that is causing some confusion)

My questions are:

1.  If I change my ESXi host to point to our internal Netware server, will it go back in time, by the 5 minutes, and does this cause any problems?

2.  When does a VM poll the ESXi host to synchronize its time? Or do I need to manually force the VM to get the new time from the ESXi host

3.  It is always best practice to sync vm's to the host, or should each vm be configured for a time source?

At this time, we have no domain controllers running, as we are not running active directory.

Thanks in advance for any assistance/suggestions

[kjb007]

NTP will tollerate up to a 5 minute skew, so as long as the time between client and server is within that timeframe, NTP will stay active.  Sync will occur with the time server, based on the polling interval you have specified.

Generally speaking, as long as your environment is sync'd to the same timesource, you will stay out of trouble.  It is when the time is different, that you can have trouble with sync'ing between host and vcenter, for instance.

The VM's only check for time based on your vmtools settings, and typically, for Windows machines would sync with domain, but since you don't have that, I would sync them with the NTP server as well.  Keep in mind though that if the skew gets too large, then NTP will stop, and time will no longer be consistent.

Best practice dictates w32time or NTP.  http://kb.vmware.com/kb/1318

[Troy_Clavell]

I have also noticed that on some of the Windows Server VM's, in the  windows o/s ntp is also configured (thinking that is causing some  confusion)

This is probably part of your problem.  Use one or the other, but not both.  You are causing a ping pong effect for NTP

1.  If I change my ESXi host to point to our internal Netware server,  will it go back in time, by the 5 minutes, and does this cause any  problems?

ESXi uses UTC as it's time, so the only time you'll see the time change is when you have the vSphere Client open, as it takes the current time of the client.  So changing your NTP source will have no adverse affect on ESXi.

When does a VM poll the ESXi host to synchronize its time? Or do I need  to manually force the VM to get the new time from the ESXi host

you don't need to manually force time, there is a polling interval, I'm just unsure of the exact time frame.

3.  It is always best practice to sync vm's to the host, or should each vm be configured for a time source?

Best practice is to use one source or the other, but never both.  For what it's worth, all our guests get their time from AD and so do our ESXi Hosts.

for Windows Guests, see also http://kb.vmware.com/kb/1318