Starting from an orginal large folder structure with subfolders, which had at least 30,000 photos. I have been creating and organising a new folder structure in light room which is very similar but not identical to the original. I have also added many photos bringing the total up to about 50,000. At the moment there some duplicates in both folders that I am about to eliminate as far as possible. However I wan't to be certain that in the process of all of this work that I have not accidentally removed importan photos. Thus I am wanting to look at the original 30,000 files to make certain that all of its photos are represented in the 50,000 set. I want to do that non destructively. I am hesitating to remove the duplicates before doing this as this is likely to further destroy the similarities between the two folder system. Thus all I want to know is what photos are in folder 1 that are not in folder 2. How should I do this automatically?
If, as you say "organising a new folder structure in light room... "- then there should NOT BE ANY DUPLICATE FOLDERS OR FILES!
Everything you did IN LIGHTROOM was a 'Move' of files and folders on the hard-drive. There should not be a Folder 1 and a Folder 2!
So please explain in great detail you exact workflow.
If you 'copied' files and folders with the OS File browser to a different structure, then I am afraid you have created a nightmare for yourself, and you would need to relink everything. Some advice in this site link- MOVING PHOTOS- 2 Methods