Report and Trend Server Redundancy
- Last UpdatedSep 07, 2026
- 2 minute read
Report, trend, and I/O server redundancy is achieved by adding standby servers within a defined cluster to provide redundant system components. Consider the following diagram:
Server redundancy of each component in the diagram is achieved by providing a corresponding standby server on the same network (LAN 1). If any of the servers become inoperative, or communication becomes inoperative, their standby counterpart assumes operation.
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For I/O server redundancy, when an inoperative I/O server comes back online, control is based on the primary or standby priority configuration for each I/O device.
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For alarm server redundancy, a main/standby model is used. For more information, see Alarms Server Redundancy.
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For trend and report server redundancy, clients try to establish a connection with the primary server at startup. If a connection with the primary server cannot be established, they will try to establish a connection with the standby server.
If an inoperative primary server becomes available, any clients connected to the standby server remain connected to the standby server unless the primary server has a higher priority. The priority is set using the connectivity parameters described below. If the standby server becomes inoperative, the client will revert to the primary server.
For more information, see Reports Server Redundancy and Trends Server Redundancy.
Connectivity Parameters
The client sub system runs in every SCADA client or server process. It connects to all servers within all clusters that are enabled, allowing any process to send data requests to any other server, either through internal systems or Cicode function calls.
Two Citect.ini parameters allow you to configure how the client sub system will manage its connections to redundant pairs of Reports or Trends servers.
These parameters are [<Type>.ClusterName.ServerName]Priority and [<Type>.ClusterName.ServerName]DisableConnection, where <Type> is the relevant server type (report or trend).
The default setting for these parameters provides behavior as described above, in that if the client sub system is redirected to a standby server it will retain a connection to that server, providing that it is operable, even when the primary server is restored. This is also the behavior that will occur if these parameters are not added for a given server type.
The connectivity parameters can be set at the system level, or specifically for each computer in the local Citect.ini file.
For a detailed explanation of these parameters see: