Hi,

First a note that OPC Classic is not my personal expertise, but this is a combination of my interpretations and I did also ask Unified Automation (that develops the UaGateway) about this, a better answer might arrive later, but this is what I can do for this now. Thus some questions and notes:

1. It is not possible to have a Classic OPC Server that would support both DA and HA, they are different specifications and servers by the nature of OPC Classic (that is one of the reasons why OPC UA was made). Thus, I believe that they would be separate servers added to UaGateway, if this “OSISoft PI HDA” would actually also have a DA server in addition to a HA server. IF that is the case, maybe the other tool can somehow give the assumption of a single server, but in reality it would have both as a separate connections.

2. What do you mean by “Write” here? An OPC UA Write? Because that cannot never work to a HA server, there is no concept of a “Write” as OPC UA Write in HA (only in DA). There is a IOPCHDA_SyncUpdate in HA for updating the history data, though that per Unified is an optional interface that UaGateway doesn’t support. It only support the IOPCHDA_SyncRead that is used to read the history. Did you mean IOPCHDA_SyncUpdate?

3. Could it be possible to produce a trace of UaGateway showing that attempt to read (AppTrace=Data, StackTrace=Debug). If is, send it to support@prosysopc.com and a note that I’ll probably need to share that info with Unified Automation.