I take pictures with a Sony mirrorless system and use Lightroom since version 5. I also use Apple devices, Ipad Pro, Iphone 7+ , Macbook Pro for pictures. As a result, I have had 12,000 + pictures between Lightroom catalog, Apple Photos, and several cloud locations such as Box and OneDive.
When the new Lightroom Classic CC and Lightroom CC were released, I decided that I needed to consolidate all photos into a new Lightroom catalog and Lightroom CC so that I can edit traditionally in Classic and in the cloud using CC for Apple Photos. When I created a new, one catalog, with pictures from the above sources, I ended up with 13,500 pictures in the new catalog with a lot of duplicates.
How do you delete duplicates from a Lightroom catalog? I did an Internet search and found a Lightroom Plugin called Duplicate Finder (https://www.lightroom-plugins.com/DupesIndex.php). What a great Plugin but how to use it? Went to YouTube and found Laura Shoe’s “Eliminate Duplicates Photos in Lightroom” (https://youtu.be/S4qpgkyql3U) which she explains how to use Duplicate Finder in a way that I could understand.
I installed the plugin and ran it. It found 3500 duplicates in my new combined Lightroom catalog. The Duplicate Finder puts the duplicates in Lightroom collection where you can go through them and keep the “best” photo for your catalog. Out of 3500 duplicates, I kept 1200.
Now, I need to create additional folders and do some key wording and I, hopefully, will have a fairly clean catalog.
I backup my Lightroom catalog to an external 4 TB drive and Backblaze (https://www.backblaze.com), a cloud-based backup system.