vSphere HA – VM Monitoring sensitivity

Last week there was a question on VMTN about VM Monitoring sensitivity. I could have sworn I did an article on that exact topic, but I couldn’t find it. I figured I would do a new one with a table explaining the levels of sensitivity that you can configure VM Monitoring to.

The question that was asked was based on a false positive response of VM Monitoring, in this case the virtual machine was frozen due to the consolidation of snapshots and VM Monitoring responded by restarting the virtual machine. As you can imagine the admin wasn’t too impressed as it caused downtime for his virtual machine. He wanted to know how to prevent this from happening. The answer was simple, change the sensitivity as it is set to “high” by default.

As shown in the table high sensitivity means that VM Monitoring responds to missing “VMware Tools heartbeat” within 30 seconds. However, before VM Monitoring restarts the VM though it will check if their was any storage or networking I/O for the last 120 seconds (advanced setting: das.iostatsInterval). If the answer is no to both, the VM will be restarted. So if you feel VM Monitoring is too aggressive, change it accordingly!

Sensitivity	Failure Interval	Max Failures	Max Failures Time window
Low	120 seconds	3	7 days
Medium	60 seconds	3	24 hours
High	30 seconds	3	1 hour

Do note that you can change the above settings individually as well in the UI, as seen in the screenshot below. For instance you could manually increase the failure interval to 240 seconds. How you should configure it is something I cannot answer, it should be based on what you feel is an acceptable response time to a failure. Also, what is the sweet spot to avoid a false positive… A lot to think about indeed when introducing VM Monitoring.