ClearSCADA can store very large volumes of historic data on a server. By default, ClearSCADA saves 52 weeks of historic data, (and 4 weeks of event journal). Once historic data is older than 52 weeks, ClearSCADA will remove it from the historian (including from disk). By default all of the historic data kept online in the system is configured as read/write. If the connection between the Main and Standby servers is broken, upon reconnection all 52 weeks worth of historic data will be resynchronized.
The servers will only synchronize historic data that is read/write. Any data that is set to read-only will not be synchronized as it is deemed to be the same in both servers. It is recommended that users set historic data to be archived as read-only after a period of a few weeks (i.e. 2 weeks). This will allow future synchronizations to occur more quickly as only the smaller data period will be synchronized i.e. in this case only 2 weeks of historic data. To mark data as read-only (available for archiving):
Go into server configuration | Historic Configuration
In the 'Historic Data' area, check the 'Archive after' box and enter the number of weeks in the field beside it, e.g. 2.
Repeat step 2) for the 'Event Journal' area, and if applicable the Alarm Summary and Configuration Changes areas.
Apply this change to the server.
Repeat steps 1) to 4) on the other server(s).
Note that further performance improvements may be gained to database startup time by reducing the historic data index memory use. By default Geo SCADA will load an index to all historic data files. If a system uses a long historic data storage time (e.g. 10 years) then consider checking the 'Index After' field and specifying a shorter period for the preloaded index (e.g. 1 year).