Insufficient configured resources to satisfy the desired vSphere HA failover level on Cluster X in Datacenter X

When configuring my vSAN cluster, I forgot to set “in case of maintenance mode, all VMs should be migrated to the other host automatically” under the HA settings.

So I made the following settings under Admission Control:

Host failures cluster tolerates is at 1, because I have a VMware vSAN ROBO Cluster. So everything was fine and I found out that the Override calculated failover capacity percentages could cause the above mentioned Problem. When I set the percentages for CPU and Memory reserved failover capacities to 5%, I received the following warning:

So the Solution was to set the Override calculated failover capacity percentage to 50% and the Warning is gone. This settings fits perfectly to my VMware vSAN Robo Cluster, which contains 2 Hosts and 1 virtual Witness Appliance. You might have enough resources to tolerate failures, but you still do not have enough resources to allow VMs to carry on with the same performance, that is what that message is trying to say.

When you are calculating available resources, consider total amount of cpu and memory reservation you have done and if 50% resource is lost, then that total reservation is still fully committed resource to corresponding VMs from your remaining available 50%, which then reduces resources for rest of the VMs and they might suffer during their peak utilization and start contending on rest of the available unreserved capacity.

And that is it from this small How-To, if you have any questions please leave a comment. 🙂