By using a pair of Application Stations, you can set up DeltaV OPC Data Access Server for redundancy. You can then configure the connection of an OPC client to the active DeltaV OPC Data Access Server so that in the event of problems, the application will recover by switching over to the Application Station running the standby DeltaV OPC Data Access Server. Switchover events include, but are not limited to:
A loss of network connectivity such that the Application Station running the standby DeltaV OPC Data Access Server loses communications integrity with the Application Station running the active DeltaV OPC Data Access Server
A planned or unplanned shutdown (or reboot) of the Application Station running the active DeltaV OPC Data Access Server
Other switchover criteria, as designed into a custom, redundant-aware OPC client
You can also manually initiate a switchover. You might want to do this, for example, so that you can retain the functionality of your DeltaV OPC Data Access Server application under the following conditions:
To upgrade your DeltaV software or other system software
To perform hardware maintenance or upgrades
To respond to an unstable or hung process on the Application Station where the active DeltaV OPC Data Access Server is running
There is a condition where both machines (the preferred active and preferred standby Application Station pair) are both in the Active state. This is called a dual active condition (sometimes called a twin active condition). While rare, this can occur when communication between the preferred active and the rest of the DeltaV network is disrupted and the pair is connected to the Plant LAN; or, the active is disconnected and reconnected while still in the active state.
This dual active condition occurs because when DeltaV detects that the active Application Station is missing from the network, it allows the standby Application Station to assume the active role. However, due to being disconnected, the status of the previously active Application Station is not updated and thus maintains its active status. When it is reconnected to (or communications resume on) the DeltaV Network, both machines of Application Station pair will be in the active state, resulting in a dual active scenario.
When this condition occurs, the expected behavior is for the preferred active Application Station to assume the active role and the preferred standby Application Station to assume the standby role.
If the option Unattended workstation reboot on failover or manual switchover is enabled, the preferred standby Application Station automatically reboots and resumes the standby role. Otherwise, the preferred standby Application Station does not reboot and is unavailable.
After setting up a pair of Application Station pair with the redundant DeltaV OPC Data Access Server feature enabled, you cannot also enable additional subsystems for these Application Stations, because they are not supported for redundant switchovers. Only assigned modules in a virtual controller, OPC Data Access Server, OPC Mirror, and Redundant DeltaV Connect can be configured to run redundantly. If you attempt to enable one of the following subsystems, a message advises that the subsystem is incompatible with redundancy:
Alarms And Events, including the Event Chronicle
Batch Historian
Batch Executive
Campaign Manager
Continuous Historian
Remote Network, including Remote Access Services (RAS) servers
It is strongly recommended that you not run the following DeltaV applications, because they are not supported for redundant operation – even if they appear in the Start menu options for DeltaV of either partner in an Application Station pair with the redundant DeltaV OPC Data Access Server feature enabled:
Auto-Update Service
To enable on the Application Station pair being used for redundant DeltaV OPC Data Access Server, run the Auto-Update Service on any other DeltaV workstation – a ProfessionalPLUS workstationstation or Operator Station, for example.
Batch Application Manager
Batch History View
Batch OI Configuration
Batch Operator Interface
Continuous Historian Administration
DeltaV Diagnostics
DeltaV Excel Add-in
Event Chronicle Administration
Inspect With InSight
Process History View
Recipe Simulator
Remote Clients
SimulatePro
User Manager
You may need to run User Manager in a Workgroup environment; however, redundancy is not supported.
Although you can start any these applications on an Application Station with the redundant DeltaV OPC Data Access Server feature enabled, inconsistent and/or erroneous data may result after a switchover. Also, running these applications may affect the stability of an Application Station where redundant DeltaV OPC Data Access Server is running.
It is strongly recommended that you not install other applications on the Application Stations where you have enabled the redundant DeltaV OPC Data Access Server feature, as these applications will not run redundantly and their operation may not be reliable following a switchover. Also, running other applications may affect the stability of an Application Station where redundant DeltaV OPC Data Access Server is running.
In particular, you should not install or use any of the following DeltaV applications on the Application Station pair: