Guest OS time advances after VMotion then retreats

[kryichek]

Today one of my physical hosts failed. HA restarted the guests on another Node in my HA cluster. I noticed that one of my guests advanced its time 1 hour then after a few minutes of running it retreated back to the correct time. What caused this?

The VMtools are NOT set to sync time with local hardware.

[dominic7]

Today one of my physical hosts failed. HA restarted the guests on another Node in my HA cluster. I noticed that one of my guests advanced its time 1 hour then after a few minutes of running it retreated back to the correct time. What caused this?

The VMtools are NOT set to sync time with local hardware.

So, how do they sync with time then?

When the system boots up it has to get time from the virtual BIOS, so even though you don't sync the time on the host system with the guests it's important to keep the host time right. After that I assume that your VM updated its time from another source like NTP or the domain.

[kryichek]

They sync time from from the domain controller. Both the domain controllers and the VMware hosts sync their time to one of our two time servers.

I verified that the host that booted the VM had the time synced properly.

[dominic7]

If you had a physical system, it would get it's time ( initially ) from the BIOS clock, it's important to remember that ESX virtualizes the BIOS and the BIOS clock time is passed from the host system time.

Is the host system's time off?

[Chamon]

If you run this on the host it will sync the system clock to the NTP time

hwclock --systohc

Find more info here

http://cmsjustin.blogspot.com/2007/09/ntp-time-synchronization-for-windows.html

[kryichek]

If you had a physical system, it would get it's time ( initially ) from the BIOS clock, it's important to remember that ESX virtualizes the BIOS and the BIOS clock time is passed from the host system time.

Is the host system's time off?

That information is good to know.

All of my Hosts in the cluster have the correct time. I havent had to re-sync any time on the phyisical hosts.