Rockwell Automation FactoryTalk Historian SE 3.0 UniInt Interface User Guide - Manual (Page 86)

UniInt Failover Scheme
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only the control points on the data source are monitored. However, values are echoed to the
Historian Server for the user to monitor. Manual failover can be accomplished by manually
changing the active ID point on the data source to the appropriate failover ID.
The figure above shows a typical network setup in the normal or steady state. This by no
means includes the myriad of configurations that are supported, it is meant to be used for an
example. If the hardware configuration differs from the figure, the settings for the two
redundant interfaces will remain the same with the exception of the /host startup
parameter. If the interfaces are communicating to a stand-alone Historian Server, the /host
parameter for both interfaces must be the same.
In order to ensure outputs to the datasource continue when a Historian Server in the
collective becomes unavailable, the interface running on IF-Node1 will need the /host
parameter set to a Historian Server that is part of the collective, and the interface running on
IF-Node2 will need the /host parameter set to a different Historian Server that is part of
the collective. The continued operation of outputs in the face of a Historian Server becoming
unavailable assumes the source data for output data (data that is read from Historian and
written to the data source) comes into Historian from a process that sends values to all of the
Historian Servers in the collective via n-way buffering.
The solid red line in the figure shows input data flow when the interface on IF-Node1 is in
the primary state. The data is read from the data source by the interface and sent to buffering.
Buffering sends the input data to all of the Historian Servers in the collective via n-way
buffering.
The solid blue line shows output data flow. Since the interface on IF-Node1 is configured
with /host=PrimaryPI, the interface signs up for exceptions with the Historian Server
on PrimaryPI. Exceptions are received by the interface and sent to the data source via the
interface.
The dashed red line shows input data flow to the backup interface. The dashed line stops at
the interface because the interface does not send the data to buffering unless the interface is
in the primary state. If the backup interface were to transition to the primary state for any
reason, the interface would send the input data to buffering. Buffering would then write the
data to all of the Historian Servers in the collective via n-way buffering.
The dashed blue line shows output data flow to the backup interface. The dashed line stops at
the interface because the interface does not send the data to the data source unless the
interface is in the primary state. If the backup interface were to transition to the primary state
for any reason, the interface would send the output data to the data source.
In the event the Primary Historian Server becomes unavailable for any reason, the primary
interface informs the backup interface that it has lost its connection to the Historian Server.
The backup interface will transition to the primary state because its status is better than the
current primary interface. If for example the entire Business Network were to go off line so
that both copies of the interface lost their connection to their respective Historian Servers.
The primary interface would remain primary because the backup interface‘s current status is
the same, not better. In this case output data would no longer flow to the data source because
there is no way for any of the interfaces to get the exception data.