Enhanced Failover is the ability to define two SCADA nodes to function as one logical node. The logical node provides data and alarms to its clients even if one of the SCADA nodes becomes inoperable. When you start iFIX on both nodes, one SCADA will be your active node, and the other will be your standby node.
The active node continuously pushes a copy of the memory-based process database (PDB) to the standby node. This process is called synchronization, by which real-time data such as setpoints, the tag database, and alarms are synchronized between the SCADA node pair. The active node synchronizes its process database with the standby node. SCADASync.exe is the iFIX application that performs the synchronization. SCADARoleMgr.exe is the iFIX application that decides if the SCADA node is active or standby.
SCADASync.exe will use any available network connection for the synchronization; however, you should prioritize network usage to separate your real-time iFIX network from the SCADA synchronization network.
IMPORTANT: It is strongly recommended that you use a dedicated network connection between the primary and secondary SCADA nodes.
When the SCADA nodes are physically close to each other, a crossover cable can be used. Additionally, it is further recommended that the network components (LAN adapters, hubs, switches, cables, etc.) used for synchronization of the SCADA pair support a minimum 1 Gigabit Ethernet.
The following figure shows an example of an Enhanced Failover configuration that includes two networks: a dedicated network for SCADA synchronization and a second network, LAN 1, which is for iFIX networking.
Simple Enhanced Failover Example: One LAN and One Dedicated Network
Operators view the process data received from a SCADA Server using an iClient. Should the active SCADA Server become unavailable, process data will become unavailable to the operator at the iClient workstation. Enhanced Failover increases the chance that data will continue to be available to the iClient, despite a failure in the active SCADA node component.
Enhanced Failover allows you to connect an iClient to both the primary and secondary SCADA Servers that are connected to the same PLC(s). The iClient establishes and maintains the connections to both the primary and secondary SCADA Servers, either of which can be the active server or the standby server. When the active SCADA Server fails and the standby becomes active, the iClient nodes automatically fail over to the newly active SCADA Server.
You can use Enhanced Failover and LAN Redundancy either individually or together. For more information, see the Examples of LAN Redundancy Used with Enhanced Failover section.
A standby SCADA will automatically take over the active role from its partner SCADA when any of the following conditions occur on the active SCADA node:
- SAC stops processing blocks due to an application exception (crash).
- The computer runs out of disk space.
- Loss of the synchronization link with the partner SCADA node. In this case, both SCADAs take on the active role.
- Loss of all iFIX network connections.
- A user requests that a role change occurs (manual failover).
- Maintenance Mode is enabled. This case occurs on the primary SCADA node.
