Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 96)

UniInt Failover Scheme
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Manual Failover
Initiating a manual failover requires that the backup interface be in a state equal to or better
than the current primary copy of the interface. For example, if the current primary has a
connection to the Historian Server and the backup does not, manual failover is not
authorized. The backup interface will know the state of the primary by the value of the
heartbeat point as explained in the next section.
Manual failover will result in overlapping data of between of up to two update intervals.
Manual failover can be accomplished by changing the value of the active ID point on the data
source from the current primary‘s failover ID to the current backup‘s failover ID. For
example, if interface copy IF1 is currently the primary and interface copy IF2 is currently
the backup, manual failover can be accomplished by changing the active ID point from a
value of 1 to a value of 2 on the data source.
If the active ID point on the data source is changed, actions taken by the interface during this
type of failover are as follows.
 The primary will notice that the value of the active ID point on the data source is equal to
the failover ID of the other copy and immediately transition to the backup state.
 Similarly, the backup will notice that the value of the active ID point on the data source
is now its failover ID and will immediately transition to the primary state.
Following is a depiction of the failover timing chart related to the manual failover scenario
where the active ID point on the data source is changed.