Virtual machine's fail to failover and remain disconnected after multiple ESXi host failures in the vSphere HA cluster

Products

• VMware vCenter Server

Issue/Introduction

• Virtual machines fail to restart on surviving hosts following a multi-node ESXi host failure in the vSphere HA cluster. 
• The vSphere HA cluster is utilizing the default 'Admission Control' setting, which is defined to tolerate only a single host failure and host failover capacity set to disabled.
• The following entries were identified in the /var/run/log/fdm.log on the master ESXi host.
  
  YYYY-MM-DDTHH:MM:SS.Z In(###) Fdm[#######] [Originator@#### sub=Invt opID=WorkQueue-########] Vm: /vmfs/volumes/vsan:###############-###############/########-####-####-####-############/VM_name.vmx (not protected) removed from local host; on 0 hosts

  YYYY-MM-DDTHH:MM:SS.Z Db(###) Fdm[#######] [Originator@#### sub=Placement opID=########] Vm /vmfs/volumes/vsan:###############-###############/########-####-####-####-############/VM_name.vmx failed placement with fault [N3Vim5Fault21NoActiveHostInClusterE:#x###############]

Environment

VMware vCenter Server 8.x

Cause

Admission Control is set to disabled for the vSphere HA cluster, resulting in insufficient reserved resources to trigger a successful failover.

Resolution

• Ensure there are valid offline snapshots of the linked vCenter VMs or in case of standalone vCenter, take a snapshot without memory.
  
  • • Snapshot Best practices for vCenter Server Virtual Machines
• Access the vCenter UI and log in using an account with administrator privileges.
• From the Inventory screen, navigate to Hosts and Clusters.
• Select the impacted Cluster from the inventory tree.
• Click the Configure tab in the main pane.
• Under the Services section, select vSphere Availability and click Edit.
• Select the Admission Control tab.
• Adjust the following parameters based on the environment's redundancy requirements:
  • Host failures cluster tolerates: Increase this value (e.g. configure it to 2 for resilience against simultaneous dual-host failures).
  • Define host failover capacity by: Choose the appropriate calculation method (e.g., Cluster Resource Percentage or Slot Policy).
• Click OK to save the changes.
• To ensure the new policy is applied correctly, disable and then re-enable vSphere HA. For detailed steps, see: [Disabling and enabling VMware vSphere High Availability].