KB2013.805
Problem: Clock drift increases over time (runaway clock), even though Domain Time appears to be correcting the clock properly

This article applies to Domain Time II.

Last Updated: 8 May 2013

Problem and Symptoms

    Domain Time Server or Client appears to be connecting to time servers and correcting the clock properly, however the amount of clock drift steadily increases. The amount of clock correction gets progressively larger after installation until a maximum drift level is reached, even though the logs show that time is being corrected to match the selected time sources/servers.

    If you view the Drift Graph on the machine and click the Raw Data button to examine the historical corrections, you'll see the Phase Adjust value steadily increasing over time. Phase adjustment normally varies within a range of +/- 50. However, machines with this problem will show increasing Phase Adjust values in the hundreds or more.

Cause

    Phase adjustment is how much the overall clock rate has been sped up or slowed down to try to match the rate of your time sources, a process known as Clock Training. Training teaches machines run at very close to the same rate as the time source clock(s), so clock corrections are minimized and time does not drift appreciably between corrections.

    However, if the right combination of latency, variability, and system load occurs on a particular machine, it can prevent Domain Time from correctly determining the right amount of clock adjustment necessary to train properly. When this happens, Domain Time will keep trying different phase adjustments to compensate for the variability, but it can end up slowly incrementing the overall Phase Adjustment value to the point where the clock is running at such a divergent speed that it becomes impossible to correct (the "Runaway Clock" state).

Solution

    Upgrade to the latest version of Domain Time. Current versions include built-in runaway clock protection.

Workaround

    If you are unable to upgrade to the latest version, you can reset and lock the Phase Adjustment value to prevent the runaway clock problem from recurring.

  1. Issue the following command from a command-prompt (elevated as Administrator) on the problem machine to reset the clock adjustment values to the defaults:

      dtcheck /resettimings

  2. Open the Domain Time applet and select the Advanced | Clock Control property page. Click the Advanced button to display the Advanced Clock Control settings dialog.

  3. On the Advanced Clock Control dialog, verify that the displayed Default Phase Adjustment value and the Phase Adjustment field value match. Then click the "Phase Locked" checkbox. This will prevent changes to the Phase adjustment by the Training function. This should bring your machine back into acceptable tolerances.

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