From OpenSCADAWiki
For the controller object of the subsystem "Data Acquisition", "Asymmetric" and "Only Alarms" reservation modes are provided. Asymmetric redundancy is working with the configuration of the controller of the remote station, as it is, and does not trying to generalize it. For this mode work all early presented functions and properties of the redundancy. The redundancy "Only Alarms" is working in fact without a redundancy, but with oppressing the alarms from the reserve controller object to exclude a duble messages in the alarms.