For details about configuring the Historian, see Configure the Historian.

High Availability Historians
The High Availability feature is intended to be used with a database system that also supports redundancy (through mirroring, clustering, or other techniques) so that any Historian in the group can update the same virtual database.

To configure failover, you create a Server Group and designate backup Historians to support a failover event. By default, no Server Group is defined. You can specify a primary Historian as well as one or more backup Historians. Only the primary Historian is capable of writing to the database.  

Each Server Group member is assigned a port number and a priority. Using a socket connection on the assigned ports, each member monitors the status of the others in the group. The member with the highest priority is elected as the primary Historian. If the primary Historian fails, is shut down, or loses its connection to the database, the backup Historian with the highest priority becomes the new primary. A Historian with a priority of 2 is has higher priority than a Historian with a priority of 1.  

For example, if we have three Historians with the following priority:

Historian A / Priority 1
Historian B / Priority 2
Historian C / Priority 3
 
and Historian C is the Primary. If Historian C is shut down, Historian B becomes the Primary. In the event of a tie in priority ranking, the Historian that was started first becomes the primary.

NOTE: Each Historian in the group should be configured with the same set of data configuration files, retention options, data source options, etc.

To configure failover for the Historian
1. Start the Historian application.

	In an initialized terminal window type: run_historian The Historian application opens.

2. Click the Server Group tab and make the following entries:

	Include in Group	Check the box to enable.
	Priority	Choose a priority for this Historian. The default is 1. The online Historian with the highest priority is the primary Historian, and updates the database.
	Port	Enter a port number on which this Historian accepts connections from other Historians in the group. The default is 3380.
	Timeout	The amount of time, in seconds, at which a connection with a group member is considered down.
	Member	For each Historian in the group, enter the hostname and port in the Member text field.

3. Click Save Configuration.