Update replicated data

Updating replicated data is very similar to updating non-replicated data with a few exceptions.

Always update data at the tier-1 Historian. The replication process then propagates the information from the tier-1 Historian to the tier-2 Historian. In other words, do not attempt to update Tier-2 data. Remember that there is some latency with propagating updated information, typically from a few seconds to a few minutes. However, bandwidth limitations and the quantity of data to be replicated may also cause delays in propagation. After propagation, all replicated tag values and their OPC qualities are identical on both tiers.

If any data modification is performed on the tier-2 Historian, including deletion of history blocks and if the data for the same tag is then modified on the tier-1 Historian and an overlapping time interval, then the data modification on the tier-2 Historian may be overwritten during replication. The replication process also creates new "patch" history blocks on the tier-2 Historian when necessary.

If some history blocks are deleted on the tier-1 Historian manually or due to scheduled disk management, the tier-2 values remain unchanged.

For more information on tag replication and replication servers, see Manage and configure replication.