OSx Station Control2-18 SIMATIC PCS 7 OSx 4.1.2 Operator
2.6 Handling a Failover
During normal operation when the system is in the Operate state, the
primary can fail. When fully implemented (hardware connections are in
place and a backup is available and active), the OSx failover feature
provides for a quick transfer of the role of primary to the designated backup.
Normal control and monitoring of the process can resume. Figure 2-4 shows
an example of a system set up for failover.
Automatic failover only occurs when the system is in the Operate state.
NOTE: A failure of the power supply for the failover feature does not trigger
failover. However, it does generate an alarm.
When a failover occurs, operators need to check the following items:
OSx station synchronization — The system determines the state of OSx
station synchronization based on the state of synchronization for the
backup when it becomes primary and the state of synchronization of
every other station. Operators need to check the
Re-Sync icon and
resynchronize their stations if necessary. Use Network Setup to
synchronize stations for the whole system.
If the backup is in sync when it becomes primary, other stations retain
the degree of synchronization that they currently indicate.
If the backup is out of sync when it becomes primary, by definition it is
now in sync, and all other stations are out of sync.
One-station utilities — After a failover from the primary to the backup,
it may be possible to run a utility, such as Network Setup, from more
than one station, even though OSx normally restricts access to the
utility to one station at a time. This can happen when the utility is
running on a non-primary at the time that the failover occurs.
To avoid this situation and to re-enable system checks for one-station
utilities, always exit the utility after a failover occurs. After exiting, the
utility will run only where normally allowed.
What Is Failover?
When Failover
Occurs
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