Insufficient configured resources to satisfy the desired vSphere HA failover level on the cluster

Products

• VMware vCenter Server

Issue/Introduction

Symptoms:

• Dedicated host fail over policy in enabled in vSphere HA cluster. 
• The cluster summary displays a message  "Insufficient configured resources to satisfy the desired vSphere HA failover level on the cluster"
• In vpxd.log, you see entries similar to (The logs below are in warning level from vCenter Server 8.0U2, but the log level needs to be verbose for below 8.0U2): 

yyyy-mm-ddT verbose vpxd[7F9A72862700] [Originator@6876 sub=DAS opID=DrsHaConfigWithTOCDialog-apply-1351484-ngc:70073575-2c-04] Failover resources reservation is 64587 cpu and 767809 memory and desired resources for admission control are 64750 cpu and 766785 memory with failover level 1

Or 

yyyy-mm-ddT verbose vpxd[10439] [Originator@6876 sub=DAS opID=xxxx] Insufficient Failover resources for admission control. Current: CPU-reservation: 120959, Mem-reservation: 476146 Desired: CPU-reservation: 120448, Mem-reservation: 476930 (failover level: 1).

Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.

Environment

VMware vCenter Server 6.5.x

VMware vCenter Server 7.x

VMware vCenter Server 8.x

Cause

1.This issue occurs if the maximum capacity host is not selected for dedicated host fail over policy

2.The resource reservations in the environment and available failover capacity are insufficient to meet the Admission Control policy requirements. Hence HA admission control fails and raises the alarm.

Resolution

To workaround this issue, use any one of the below options as per the 

• Use other admission control policies (slot or percentage based policy).
• Use host with maximum CPU and Memory among all the hosts as dedicated host.
• If failover capacity cannot be increased, consider disabling Admission Control so HA can function without strict reservation requirements.

Additional Information

When using the slot policy, vSphere HA performs admission control through the following steps:

• Calculates the slot size: A slot represents a logical unit of CPU and memory resources, sized by default to meet the requirements of any powered-on virtual machine in the cluster.
• Determines the number of slots per host: vSphere HA calculates how many slots each host in the cluster can accommodate.
• Determines the current failover capacity: This represents the number of hosts that can fail while still providing enough slots to power on all existing virtual machines.
• Compares the current and configured failover capacities: If the current failover capacity is lower than the user-defined configured failover capacity, admission control prevents the operation.

Please refer to the docs below for more information:
https://techdocs.broadcom.com/us/en/vmware-cis/vsphere/vsphere/8-0/vsphere-availability/creating-and-using-vsphere-ha-clusters/vsphere-ha-admission-control/slot-policy-admission-control.html