We are pondering what the benefits and drawbacks are of using OPC HDA verses an OPC-DA UFO pair.
As far as we can see, with DA configured for UFO and setting all tags as advise rather than polled, there is little chance of missing data values and if a significant data gap does occur, an HDA interface could then be manually used in History Recovery mode to fill it in.
OPC HDA seems to us likely to have more of a performance overhead in continual use since the OPC server must check for historical values on each scan. The default group size with HDA is also 1, which surely means far more network communications as well. What are the reasons for and against changing the group size to a few hundred?
If we have both options, we are thinking that a UFO DA interface is the better way to go. Are we wrong?