A failback operation will not complete if a host in the cluster is offline or faulty.
Possible Scenarios Resulting in Failure
Scenario 1
In a multi-node cluster, if one node is faulty then failback will not start.
Scenario 2
In a multi-node cluster, all hosts are healthy but one node's IO filter is unavailable. Failback will not start.
Possible Scenarios that Could be Successful
Scenario 3
In a multi-node cluster, all hosts are healthy but one host is in maintenance mode. Failback will continue.
Scenario 4
In a multi-node cluster, one host is faulty and that host is replaced with a healthy host. Failback will continue.
Scenario 5
In a multi-node cluster, if one host is faulty and that faulty host is removed from the cluster (remove from inventory). Failback will continue.