Time synchronization between VM and ESXi host question

[thomasross]

According to KB 1189, vmware tools synchronizes the VM's time after specific events, such as vmotion, snapshots, etc... Is this something we want to disable??

Our AD expert is advocating  following this KB article to completely disable time schronization between the guest OS and the ESXI host. Is this a good or bad idea?

I have alwasy had the time synched  within the guest OS by w32time or ntp and use NTP  for synching the ESXi hosts , and disabled the time sychronization between the VM  and the ESXI host. And have never had any problems with time synch.

Now this person is claiming becasue the VM will time synch to the ESXi hoast under certian conditions, this will casue the VMs to get out of synch and advocates following 1189 to completely disable this feature.. Should we do this?

[DavoudTeimouri]

Hi,

When you have Windows OSes as client/server and they are joined to a Windows domain. The clients time will be synced with domain controller automatically.

So disabling VMware Tools time synchronization is recommended.

But add a NTP server address for syncing your ESXi time with that for ESXi logging.

[JarryG]

"VMware recommends using NTP instead of VMware Tools periodic time synchronization."

You can find this statement in a few KBs, for a good reason. So our AD-expert is right: disable time-synchronization in vm-tools, and use only ntpd.

[thomasross]

Thanks, That is what I thought.

Is there any case where you would want to totally disable the time synch between the VM and ESXi host? for example when vmware tools starts or a vm migrates to another host, etc… the VM will temporarily get its time synch form the host. Is there ever a reason why we would not want to do this?

Thomas Ross

[Dee006]

Thomas,

VMware has couple of best practice KB and articles list below

http://www.vmware.com/files/pdf/Timekeeping-In-VirtualMachines.pdf

VMware KB:    Timekeeping best practices for Windows, including NTP

Hope this would help for better understanding and your find own solution.

[cykVM]

I just had a troubleshooting case at a customer site. Someone played around with the ntpd settings on the ESXi host and time started drfting on every special event (e.g, reboot of the VM(s)). I then found out that he also had some kind of historic settings in ESXi host config for DNS pointing to a non-existing server.

You should have a DNS setup on the host pointing to a reachable DNS even a boottime of the host for ntpd on the host to work correctly.

Besides Active Directory, which sooner or later starts to run mad if the time is drifting you may run into serious trouble with Exchange server(s) which won't mount their Mailbox datastore anymore.

Since the host was running on a HP Proliant with an iLo 4 card, I also put up time synchronization with ntp on the iLo to the onboard hardware clock. Now everything is in place and running well.

To check ntpd on the host is working correctly I followed this KB: VMware KB: Troubleshooting NTP on ESX and ESXi 4.x / 5.x