Alarm reporting further restricts when a condition or state alarm trigger occurs by adding a tolerance range and a trigger frequency to the trigger configuration.

The tolerance range specifies a percentage above or below the configured threshold point, after which the alarm triggers or clears. A nonzero value triggers and clears the alarm only after the triggering condition falls above or below the tolerance range. A 0 (zero) value triggers and clears the alarm at the threshold point you configured.

vCenter Server uses the following calculation to trigger an alarm:

Condition threshold + Tolerance Range = Trigger alarm

For example, an alarm is defined to trigger a warning state when a host’s CPU usage is above 70%. If you set the tolerance range to 5%, the warning state triggers only when CPU usage is above 75% (70 + 5) and resets to a normal state only when CPU usage falls below 65% (70 - 5).

The tolerance range ensures you do not transition alarm states based on false changes in a condition.

The trigger frequency is the time period during which a triggered alarm action is not reported again. When the time period has elapsed, the alarm action occurs again if the condition or state is still true. By default, the trigger frequency for the default VMware alarms is set to 5 minutes.

For example, if the Host CPU Usage alarm triggers for a warning state at 2 p.m. and an alert state occurs at 2:02 p.m, the alert state is not reported at 2:02 p.m. because the frequency prohibits it. If the warning state is still true at 2:05 p.m., the alarm is reported. This guards against repeatedly reporting insignificant alarm transitions.