This Knowledgebase article provides information about the Neverfail architecture.
The product includes a replication component, which ensures data changes that occur on the active server are replicated to the passive server. However, this replication component is only a piece of the overall solution. For replication, we ensure that only file changes, not entire files, are replicated from an active to a passive server thus keeping replication traffic between systems to a minimum. We do not introduce any delay into transaction processing on the active server as we asynchronously replicate data between systems.
In addition to the above, Neverfail Heartbeat can pro-actively monitor the protected application and system resources of the server it is installed on. When pre-determined levels have been reached Neverfail can then be configured to perform a number of actions automatically or to warn the Systems Administrator via email.