Access to the Fault Tolerance metadata datastore is essential for the proper functioning of an FT VM. Loss of this access can cause a variety of problems.
These problems include the following:
FT can terminate unexpectedly.
If both the Primary VM and Secondary VM cannot access the metadata datastore, the VMs might fail unexpectedly. Typically, an unrelated failure that terminates FT must also occur when access to the FT metadata datastore is lost by both VMs. vSphere HA then tries to restart the Primary VM on a host with access to the metadata datastore.
The VM might stop being recognized as an FT VM by vCenter Server. This failed recognition can allow unsupported operations such as taking snapshots to be performed on the VM and cause problematic behavior.
Lack of access to the Fault Tolerance metadata datastore can lead to the undesirable outcomes in the previous list.
When planning your FT deployment, place the metadata datastore on highly available storage. While FT is running, if you see that the access to the metadata datastore is lost on either the Primary VM or the Secondary VM, promptly address the storage problem before loss of access causes one of the previous problems. If a VM stops being recognized as an FT VM by vCenter Server, do not perform unsupported operations on the VM. Restore access to the metadata datastore. After access is restored for the FT VMs and the refresh period has ended, the VMs are recognizable.