There is no practical hard limit to the number of items (tags) that OPC Toolbox can transfer to/from a server. Our practical experience indicates the following:
+ With a large number (>10,000) of items, creating the item array can take some time (minutes) if the server is non-local. There is a lot of communication taking place between the server and client machines, and that is dependent on too many factors to mention (but response times from a "ping" between the server and client is a good first step). This communication overhead is high when creating items, but becomes much lower once the items are configured.
+ If you have a large number of items in a Simulink model, you will have to set the "Pseudo real-time violations" setting to "None" (in the OPC Configuration block) as the time taken to set up the items makes any other setting impractical.
+ Rather than configure a single group containing all the items, in one case we have seen success with many groups containing a smaller number of items each (e.g., instead of 1 group with 1000 items, create 10 groups with 100 items each). However, we have not done any specific benchmarking locally. This approach works equally well whether you are using MATLAB or Simulink.
Unfortunately with OPC there are many variables, but the most important is probably network communication rates between the client and server machines. Keep in mind that the client actually does very little processing, relying instead on messages from the server.
