Applies To:
  • CitectSCADA

If a Citect for Windows client is communication with the Primary Citect server and that server fails, the Client will switch to the Standby Server. When the Primary server restarts, the Clients will stay on the Standby Server, unless the Standby server fails, or the client is restarted. 

Citect does this to save the extra overhead of checking if a primary server has come back online, and also because Client does not care if it is connected to the Primary or Standby server - they are both maintained the same.

Because of this operation it is quite normal for some clients to be communication to the primary and some to the Standby server.

Note also that this operation only occurs for the Reports, Alarms and Trend server. The I/O Servers redundancy is handled on an individual I/O Device Basis. If a Primary I/O Device fails, the clients will use the Standby I/O Device, but when the primary I/O device comes back online the clients will switch back to the primary I/O Device.