In OPCDA service group Under Special configuration tab, what is significance of ALLOW PARALLEL REDUNDANCY ?
In manuals it is mentioned to be keep Unchecked.
Significance of this option in 800M and MOD OPC ?what will be the effects if we keep this option (ALLOW PARALLEL REDUNDANCY) enable or checked ?
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- Default: enabled
- MOD300: disabled
When enabled, a small subset of client types (SoftAlarm, Basic History, ...) will have each single service provider to run its subscriptions over BOTH connectivity servers.
This enable them to perform ULTRA FAST failover in case one feed is disrupted. Normally, a failover takes a few seconds to effectuate (moving all the OPC items from one CS to the other).
Most OPC servers (excluding MOD300) are capable of multiplexing OPC items to multiple clients having them subscribed. Meaning no extra traffic with the controller.
Eg: Basic History has 100 items logged over a redundant AC 800M CS pair (CS21+CS22). With Parallel Redundancy enabled, the OPC DA Connector in CS21 will receive 100 items from the local historian, but ALSO another 100 items from the historian in CS22. And vice versa in CS22.
Each AC 800M OPC server will receive 200 items, but since they are two identical sets of the same 100 items the EFFECTIVE subscription (after multiplexing) towards the controller will ONLY be 100.
Ergo: OPC servers unable to multiplex identical OPC items (such as MOD300) should have Parallel Redundancy disabled.