"Insufficient resources to satisfy configured failover level for vSphere HA" error when Powering ON a Virtual Machine

Products

• VMware vCenter Server

Issue/Introduction

• Power ON task on a Virtual Machine fails with error "Insufficient resources to satisfy configured failover level for vSphere HA".
• vSphere HA is configured on the cluster with Admission Control enabled.
• The Virtual Machine has resource reservation for CPU.
• The issue may also be seen when an ESXi host goes into not-responding state and there are not enough resources in the cluster to power on the Virtual Machines.

Environment

VMware vCenter Server 8.x

VMware vSphere ESXi 8.x

Cause

• The ESXi hosts in the cluster do not have enough resources to satisfy the Virtual Machine resource requirement causing the Power ON task to fail.
• The two conditions below cannot be satisfied simultaneously:
  • Virtual Machine Resource Reservation: The specific CPU or memory reservation required by the VM attempting to power on.
  • HA Failover Capacity Guarantee: The resource buffer required to satisfy the cluster's configured failover tolerance (e.g., "Percentage of Cluster Resources," "Slot Policy," or "Dedicated Failover Hosts").
• When a Virtual Machine with a reservation attempts to power on, Admission Control calculates if accepting the VM will violate the pre-configured HA failover capacity setting.
• If the required Virtual Machine reservation, when added to the current resource consumption, leaves less than the guaranteed HA failover buffer, the power-on task fails.

Resolution

• Evaluate and Adjust Resource Utilization:
  The cluster is operating at high utilization and cannot tolerate a host failure while satisfying all reservations. Action must be taken to create more available capacity by:
  
  
  • Increasing Cluster Resources:
    Add one or more new ESXi hosts to the cluster to significantly increase the total CPU and memory available.
  • Reducing/Removing VM Reservations:
    Identify non-critical VMs with high CPU or memory reservations and reduce or remove these reservations. Reservations should only be used for critical workloads that absolutely require guaranteed resources.
  • Adjusting HA Failover Capacity:
    If the failover requirement is set too high (e.g., guaranteeing 25% of resources), consider adjusting it downward if the business requirement allows (though this is often the least preferred option).
    
    
• Workaround:
  Temporarily disable vSphere HA Admission Control to bypass the resource guarantee check.
  This will free up the failover reservation resources, allowing the Virtual Machine to power on.
  
  
  • Navigate to the Cluster in vCenter Server.
  • Go to Configure -> vSphere Availability -> Edit.
  • Under Admission Control, change the setting for "Define Host failover capacity by" to the "Disable" option.
  • Power ON the Virtual Machine.