Virtualizing NTP server

Question

Possible Duplicate:
What are the limits of running NTP servers in virtual machines?

I was wondering if virtualizing NTP is okay. I have a VMware ESXi 5.0 box, and I want to virtualize my router since the original hardware bit it. The only thing is I have read in places that virtualizing NTP (which my router performed) was not good because you won't be as accurate as a hardware clock. Is this true?

My router was pfSense, it ran the OpenNTPD server and was pointed at tock.usno.navy.mil. Because I am syncing with a higher NTP server is the accuracy of the hardware that important?

Answer 1

This has been addressed before: What are the limits of running NTP servers in virtual machines?

Short answer: Don't do it. The accuracy of your local clock is still important when setting up an NTP server, and there are too many variables when using virtual machines to guarantee reasonable accuracy.

Answer 2

Depends on how accurate you need the clock to be. The Virtual Clock provided by the VM will have an inconsistent slew; usually this is limited to milliseconds. So your VM may have a hard time keeping track of it's slew in greater accuracy than ~0.1s. For most applications this is plenty accurate enough.

For certain software/hypervisor combinations the inconsistent slew causes problems and the time eventually gets off by a large amount. I've never seen this problem with ESX however.

For all platforms be certain the VM's clock is not synched to the hardware clock. There's an option to disable this as it's normally enabled. The VM will constantly have the wrong time if the hypervisor is overriding NTP.

On a side note: There are restrictions on using the cluster (tick, tock, and ntp) at usno.navy.mil; unless you meet certain qualifications you should not be using it. You should be using Stratum 2 servers, such as the pool.ntp.org project.