Rockwell Automation FactoryTalk Historian SE 3.01 Installation and Configuration Guide - Manual (Page 128)

Appendix A Configuring Historian Servers in High Availability Mode
128 Rockwell Automation Publication HSE-IN024A-EN-E–December 2012
If you have an insufficient number of the license activations
that need to be assigned separately to the primary and
secondary server in a collective, you are prompted to reassign
the licenses.
7. Click Apply. The license activations are saved.
To implement HA, configure interfaces to support failover and
n-way buffering. Failover ensures that time-series data reaches the
Historian server even if one interface fails; n-way buffering ensures
that identical time-series data reaches each Historian server in a
collective.
To support failover, install a redundant copy of an interface on a
separate computer. When one interface is unavailable, the
redundant interface automatically starts collecting, buffering, and
sending data to the Historian server. To support n-way buffering,
configure the buffering service on interface computers to queue data
independently to each Historian server in a collective.
In some deployments, interfaces send outputs (that is, data from the
Historian server) to the data source. With a proper configuration,
failover considers the availability of the Historian server for outputs
in addition to the availability of the interface.
NOTE
For more information, refer to the FT Historian High Availability
Administrator Guide, chapter "Interfaces".
Configuring Interfaces and
Buffering Services for
Historian Server Collectives