A Warm Failovermode is where the Clientshould connect to one or more Serversin the Redundant Server Setprimarily to monitor the ServiceLevel. A Clientcan connect and create Subscriptionsand MonitoredItemson more than one Server,but sampling and publishing can only be active on one Server. However, the active Serverwill return actual data, whereas the other Serversin the Redundant Server Setwill return an appropriate error for the MonitoredItemsin the Publishresponse such as Bad_NoCommunication. The one Active Servercan be found by reading the ServiceLevel Variablefrom all Servers. The Serverwith the highest ServiceLevelis the Active Server. For Failoverthe Clientactivates sampling and publishing on the Serverwith the highest ServiceLevel. Figure 30illustrates the steps a Client would perform when communicating with a Server using Warm Failovermode.


Figure 30– Warm Failover

NOTE There may be a temporary loss of data from the time the connection to the Active Serveris interrupted until the time the Clientgets Publish Responsesfrom the backup Server.