ESX Servers and Time Synchronization

[sdibias]

Can any of you point me in the right direction regarding ESX and Time Synchronization in an Active Directory Domain environment. As of right now the PDC Emulator is Synchronizing with an external time source, and all of the worksations and member servers Synchronize with the PDC Emulator. How will this change with the inception of ESX & VI3? I have read different scenarios and options for time synchronization with ESX, however I'm not entirely sure how we should proceed. Thanks in adavance!

[admin]

You can still sync the VMs with an external time source, it works fine, alternatively you can sync the ESX hosts with the external time source and then sync the VMs with the hosts via VMware Tools.

Have a read of this: http://www.vmware.com/pdf/vmware_timekeeping.pdf

[sdibias]

I only ask becuase some of what I have read regarding time synchronization says that one choice is better than the other. It looks like the VMware best practice is to have the ESX servers synchronize with an external time server, and then have the VM's hosted on the ESX servers synch with the host using VMware tools. Obviously we could have the VM's synch to the Domain Controller and then configure the ESX servers to synch with an external time server, however I have read that this scenario can be problematic. According to what I have read with this solution is that computers running inside a virtual machine do not realize they are in a virtual world. Periodically the VMKernel may need to swap a VM out of CPU in order to balance loads as specified in the Resource Pools. When a VM swaps back in, its clock will be incorrect. The guest OS will not realize that it is behind. the correct time. It will resynchronize eventually, but time will be incorrect until it does.

With that being said I'm thinking we will go with having the VM's synch to the ESX servers. Please comment if you have any other input on this subject. Thanks

[wallboy_]

i had had a few problems with the time sync in a previous enviroment. I found the best was was to sync the ESX server with the DC, but my DC's were not VM's if you have your main DC as a VM then things can get a bit strange. Alternativly just dissable the sync time with ESX server option in the VMWare tools. I had 200 VM's so i couldn't do this.....

[johnswb]

I've had the same question and the best application is depending on who you talk to. I have it both way and have had success in both. It's going to come down to, what makes you feel comfortable. Currently we have several DC running as vm's and a couple running on physical boxes, and pointing all (host, vm's & physical machines) to an external source. I have had this in place for more then two years now and have not had a problems with time.

[dkfbp]

Hi,

We have a large enviroment with several hundreds of virtual machines in our active directory.

We don't sync the guests with the esx hosts but with the AD. The PDC syncs from an external

time source.

This has worked without any problems for us.

Best regards

Frank Brix Pedersen

[wallboy_]

All realy depends on the enviroment. Most of my enviroments are in DMZ's and so NTP out is normaly blocked, Thats why i do it on the DC's

What external sources do people use?

[J-D]

We use NTP servers from ntp.pool.org

You will find NTP servers in your region on their site. You have continent pool servers too.

Eg: eu.pool.ntp.org for Europe and be.pool.ntp.org for Belgium. We use 0.be.pool.ntp; 1.be.pool.ntp.org and 2.be.pool.ntp.org

Plenty of choice and ISP independant.