When should I use the Mirror Service instead of Dual Logging?

Typically we would favor dual logging over the Mirror Service.  However, the Mirror Service can be very useful for the following use cases...

1. To capture Axiom Annotations. Annotations are saved with HDB2 files and those files must be sent to the machine currently in use to see the annotations that were assigned to those tags from that machine's Axiom portal?

 
2. To push data from a remote historian with a weak cellular or satellite connection to a corporate historian. The Mirror allows you to schedule the 'pulls' or 'snapshots' of the local historian as well as apply bandwidth constraints to the movement of the data.

3. Capturing data from large numbers of historians already in the field without requiring the reconfiguration of logging configurations.  Some organizations may already have tens or hundreds of logging sessions configured at remote sites and it could be impractical to reconfigure all of those sessions.  The Mirror would allow for a faster deployment to centralize the data.

Limitations of the Mirror Service are due to Events and Calculations.  Since the Mirror is designed to pull data at a scheduled time, Events and Calculations cannot be run in real-time on a historian that is using the Mirror to snapshot data from other historians.

Eric Trexler  I added a few thoughts