View Legacy Data
Applications that were in use and logging data prior to the introduction of the Historian tag will have legacy data. The Historian tag can read this legacy data, but it must be configured to do so.
Three application properties are used by the Historian tag to find legacy data. The property, UseLegacyHistoryPriorTo will be configured for you when you convert an older application to the current format but, you may need to adjust the values for your particular application.
Sets a time stamp marking the latest date and time that legacy data was recorded. This will usually be the moment that the application was converted from one system to the other but, if your application is configured to use a time-delay when logging data, then you may need to adjust the UseLegacyHistoryPriorTo value to account for the offset.
Required only on a workstation that does not have its own copy of the data. Typically set to a network path, identifying the machine and the folder (usually "History") where the legacy data is stored.
This legacy property predates the Historian tag. If present, it should be left unchanged.
Legacy data is not synchronized between servers in a multi-server application. It exists only on the computers that you explicitly copy it to. You should copy it to the primary server and all backup servers to ensure that the data is continuously available. In a multi-server application, copy the data from whichever server is deemed to have the most complete copy of the data.
Should a workstation client lose its connection to all servers, it will not have access to the legacy data.
