Daemon Down Node Alive (DDNA) is a condition in which the VCS high availability daemon (HAD) on a node fails, but the node is running. When HAD fails, the hashadow process tries to bring HAD up again. If the hashadow process succeeds in bringing HAD up, the system leaves the DDNA membership and joins the regular membership.
In a DDNA condition, VCS does not have information about the state of service groups on the node. So, VCS places all service groups that were online on the affected node in the autodisabled state. The service groups that were online on the node cannot fail over.
Manual intervention is required to enable failover of autodisabled service groups. The administrator must release the resources running on the affected node, clear resource faults, and bring the service groups online on another node.
You can use the GAB registration monitoring feature to detect DDNA conditions.