What is my SCADA Role?
Each node in an Enhanced Failover SCADA pair has a role: Active or Standby. In normal operations, one SCADA assumes the Active role, and the other SCADA assumes the Standby role.
If a SCADA node cannot communicate or detects a problem with its partner, it becomes the Active node. If both SCADA nodes are Standby or both nodes are Active, the Primary node becomes Active. When using Maintenance Mode, both SCADAs will be Active.
Roles can also be changed manually by changing values of the NSD (network status display) tag: A_SWITCHSCADAROLE or F_SWITCHSCADAROLE. The NSD tag provides the ability to force a SCADA to a particular role or to display information about the SCADAs or Clients.
Summary of When Role Changes Occur
A SCADA role automatically changes when:
- SAC stops processing blocks due to an application exception (crash).
- The computer runs out of disk space.
- All synchronization links between the two nodes are unavailable.
- A user requests that a change occurs (manual failover).
- iFIX connectivity is unavailable. For instance, this scenario occurs when disconnecting the iFIX networking cable on the SCADA computer. Be aware that a SIM is needed to support this functionality.
NOTE: SCADA roles do not change as a result of bad Driver to PLC communication.
