PI to PI history recovery

You can use history recovery to recover data for time periods when PI to PI was not running or could not collect data. You can configure the history-recovery period. The default value is eight hours. You can also specify a start time and end time to recover history from a specific time range. You use this technique to transfer data from one server in a Data Archive collective to another server in the collective when interfaces cannot send data directly.

If you use n-way buffering to write data from the PI to PI interface to a Data Archive collective, history recovery requires that all target servers be in the same initial state. Upon startup, PI to PI checks the snapshot value on the target Data Archive server for each tag in its tag list. PI to PI uses the snapshot value to determine the starting time point for history recovery. However, PI to PI only checks the snapshot value at the target server specified in its startup file (the host server). If the values are not the same at other servers in the collective, the single starting time point will result in either a data gap or a data overlap. To avoid this situation, initialize each Data Archive in the target collective with the same set of data before implementing the PI to PI interface.