# Run the Distributed Index Handler in Mirror Mode

In mirror mode the DIH distributes all the index data it receives to all the connected IDOL Servers. The IDOL Servers are exact copies of each other and must all have the same configuration.

Run the DIH in mirror mode to ensure uninterrupted service if one of the IDOL servers fails. If one IDOL Server is inoperable, its identical copies continue to index data and return data for queries.

The DIH periodically checks if all the connected IDOL Servers are operating. If an IDOL server fails, the DIH queues the data that this IDOL Server normally receives. When the IDOL Server starts operating again, it indexes the queued data into it.

To run the DIH in mirror mode

1. Open the DIH configuration file in a text editor.

2. Find the `MirrorMode` setting in the `[Server]` section and set it to `True`.

3. Save and close the configuration file.

4. Restart the DIH for your changes to take effect.

NOTE: When you change the `MirrorMode` configuration option to enable or disable mirror mode, you must also delete the `Main/` subdirectory in the DIH installation directory.

This additional action prevents accidentally switching between mirror and non-mirror mode, which can cause a loss of data. If you do not delete the `Main/` directory when you change the `MirrorMode` option, DIH does not start.

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