5 Replies Latest reply on Jul 13, 2018 2:19 PM by nthorson

    OPC Interface Warm Failover and Advise tags


      In the  OPC Int User Guide on page 64, it lists the following information about Warm fail over.

      Warm_1: Do not create groups on the server (/fm=1)

      Warm_2: Create inactive groups and add PI points (/fm=2)

      Warm_3: Create active groups; do not use advise groups (default)

      What is unclear to me is option 3.  It says "do not use advise groups".  Does that mean we cannot use advise tags with Warm 3 fail over?

        • Re: OPC Interface Warm Failover and Advise tags

          Hi Nick,


          In relation to the data flow, there is the flow as DCS/PLC -> OPC Server -> PI OPC Int

          The groups in the user guide mean the groups in OPC Server. In warm_3 type, there are active groups created with tags configured. This means that OPC Server will have an active load to fetch values from its data source.

          But PI OPC Interface is not subscribed to the group (so opc server does not give values to PI interface) because it is in the backup state.

          In transition, Warm_3 would be the quickest out of warm ones to failover. But if you can make a use of warm3, then you might as well go for a hot failover to achieve no data loss.

          Notes on Phase2 trade-off: Data Loss vs. Load on OPCserver

          COLD ------------ WARM_1 -------------- WARM_2 ------------- WARM_3 ------------------ HOT

          No Load ---------------------------- (more Load) ------------------------------> most Load

          most Data-loss ------------------ (less Data-loss)--------------------------> no Data-loss

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            • Re: OPC Interface Warm Failover and Advise tags

              I understand the difference between hot, warm, and cold.  What I am asking is can I use advise tags with warm 3 fail over?  The excerpt from the OPC Int user manual show above seems to imply I cannot.  However, it is not clear.

                • Re: OPC Interface Warm Failover and Advise tags

                  Hello Nick-


                  Yes, you can use Advise tags with Warm_3.


                  Warm_3 will connect to the OPC server, create groups, add Items, and activate the groups, but will not advise the groups. This means that the OPC server is obligated to keep its cache of current values for all the

                  items updated, but it need not send the values to the interface. If both interfaces are connected to the same server, and the server maintains one central cache for data, this may be almost no additional load on the server, since the cache must be kept updated for the primary interface anyway. But for a server that does not use a centralized cache, or where the interfaces connect to different OPC servers, this can be a considerable load on an OPC server or on the backend system.


                  The user guide text is flawed. I will have that changed.





                  1 of 1 people found this helpful
                  • Re: OPC Interface Warm Failover and Advise tags

                    If tags are set to advise, then it will get advise from OPC Servers. So if tag configurations are correct, then you can use advised tags with Warm 3 failover or with any failover modes.

                    Hot/Warm/Cold failover applies to the instance that is in a backup state. Once they go to primary state, then they will gather data according to the tag configuration.