Redundancy and RealTime failovers

Open Platform Communications (OPC) does not have intrinsic support for redundant servers and failovers between them. However, the AVEVA OPC server is configured to run as a redundant pair if the RealTime service is itself redundant.

OPC clients connect to the virtual RealTime hostname, so they always obtain a connection to the Hot RealTime OPC server. If the OPC client attempts to connect to the Standby OPC server, the standby server will refuse the connection. It is advisable for an OPC client to always connect to the virtual RealTime IP address, as this automatically and correctly routes them to the OPC server on the Hot RealTime box. In the case of a failover, the OPC server on the failed computer shuts down in order to ensure that OPC clients cannot keep a connection to a server that is no longer active.

The OPC client is responsible for detecting any OPC connection failures and must then reconnect and resubscribe to the desired points.

AVEVA Enterprise SCADA supports change in point ownership (DistribuSys). If the OPC client has a connection to a AVEVA Enterprise SCADA system that does not own the point that the OPC client is reading, the OPC client will receive the data that was replicated from the owning system to the non-owning system.

If the OPC client writes a data value to a non-owned point and the AVEVA Enterprise SCADA system has configuration and control privilege for the non-owned point, one of the following will occur:

• The AVEVA Enterprise SCADA Business Logic Tier (BLT) software will replicate the written value to the owned system and other non-owned systems.

• The change will be made directly on the owning system and replicate the change out to all non-owning systems (the decision on where to make the change and how to replicate it is configured for each RealTime database (RTDB) field).