If VM Component Protection (VMCP) is enabled, vSphere HA can detect datastore accessibility failures and provide automated recovery for affected virtual machines.
VMCP provides protection against datastore accessibility failures that can affect a virtual machine running on a host in a vSphere HA cluster. When a datastore accessibility failure occurs, the affected host can no longer access the storage path for a specific datastore. You can determine the response that vSphere HA will make to such a failure, ranging from the creation of event alarms to virtual machine restarts on other hosts.
When you use the VM Component Protection feature, your ESXi hosts must be version 6.0 or higher.
Types of Failure
There are two types of datastore accessibility failure:
PDL (Permanent Device Loss) is an unrecoverable loss of accessibility that occurs when a storage device reports the datastore is no longer accessible by the host. This condition cannot be reverted without powering off virtual machines.
APD (All Paths Down) represents a transient or unknown accessibility loss or any other unidentified delay in I/O processing. This type of accessibility issue is recoverable.
VM Component Protection is configured in the vSphere Web Client. Go to the Configure tab and click vSphere Availability and Edit. Under Failures and Responses you can select Datastore with PDL or Datastore with APD. The storage protection levels you can choose and the virtual machine remediation actions available differ depending on the type of database accessibility failure.
Under Datastore with PDL, you can select Issue events or Power off and restart VMs.
The response to APD events is more complex and accordingly the configuration is more fine-grained. You can select Issue events, Power off and restart VMs--conservative restart policy, or Power off and restart VMs--aggressive restart policy
If either the Host Monitoring or VM Restart Priority settings are disabled, VMCP cannot perform virtual machine restarts. Storage health can still be monitored and events can be issued, however.