NTP settings. My boss wants to run the guests on a NTP server, I want them to sync with the host.....Need an argument to convince him

[GodTheHamster]

Ok, so my boss wants the guests to sync with a time server, ive told him that they should sync with the host to avoid CPU contention and missing ticks causing time drift. He dosnt care, says the OS should sync with an outside source and wont care what the hardware is doing. however its the hardware that controlls the frackin time. So if the CPU cant tell the OS to change its time its not going to.

This would then cause issues with AD, SUS, SEP, bascially everything on our network.

However we have a relativly small environment and nothing on the host so far is very CPU intensive.

Anyhow. I need a good argument to convince him that we should let the host handle the time.

This is a guy who thinks that setting DHCP reservations is the incorrect way to use DHCP and wants to change the scope and static everything on the network. So why should i let VMtools sync time with the Host? Or why shouldnt I. cant find anything pointing to using NTP servers. everything just says use the Host.

[a_p_]

From what I understand you have an AD running!? If so, the time sync of the AD members should not be done against the host nor an external NTP source. The AD members - by default - sync their time with the DC's. Only the DC's should be configured for a reliable time source. What I do is to sync the time of the DC's with an external NTP server and configure NTP on the ESX(i) hosts to use the DC's.

André

[scowse]

If the vm guests are domain machines then they should get their time from a domain controller (which gets its time from ntp servers)

The esxi host machine should get its time from ntp

[GodTheHamster]

So we are both wrong? :smileysilly:

Just leave the guests alone and make sure the DC is getting its time from NTP (which is currently is)

[Rumple]

vmware has a very good timekeeping document

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1318

Long and short:

Host - NTP Server

Windows VM

Windows Version	Recommended Time Sync Utility
Windows 2008	w32time or NTP
Windows Vista	w32time or NTP
Windows 2003	w32time or NTP
Windows XP	NTP
Windows 2000	NTP

Funny enough we had this discussion at work...we eventualyl came to this conclusion

Pick ONE...

In the end it doesn't appear to matter which you choose except in extreme oversubscription instances if you use NTP, w32time or vmware tools...

In the end It really matters that you don't mix/match...

[AureusStone]

I would recommend not using VMWare tools to sync the time.

If the time on the guest goes ahead of the host time, the time will not be fixed.  VMWare tools will only correct time that drifts behind host time.

This is a big limitation and I have personally seen it go wrong before.

[grasshopper]

Check out the new KB with some nice little vmx hacks:

http://kb.vmware.com/kb/1189

We certainly could have used this years ago.  Better late than never!

[depping]

You should sync with NTP or AD or whatever and not with the host itself. That is an outdated best practice. Reason for this being, as mentioned above, is that only when you are "behind" it will fix it... when time is running too fast it won't. NTP or w32tm is the way to go.

Duncan (VCDX)

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