to commonly asked questions.

Moved data from one drive to another but sizes are not equal.

I dragged and dropped all files (photos library, movies, file folders with photos , mp4 files) from 1 TB Ssd to the 2 TB ssd to copy. I checked the storage on both after it was finished and the 1 TB ssd (original wrongly formatted one) had 413 GB on it and the 2 TB ssd only had 226GB. Why is that? When I checked the manage storage bar graphs on each ssd the 1TB ssd had 375 GB under other and 28 GB in photos and 9GB in movies, whereas the copied 2TB ssd had breaks it down as 112 GB of photos and 110GB of movies. The files listed under each ssd looks exactly the same as the other. I am reluctant to erase the 1TB ssd until I know it’s safe to. Is it safe to move forward?

Definitely further investigation needed here. You could compare manually folder by folder being very thorough and hopefully find the discrepancy. You could try one of my fav tools from omnigroup called omnidisksweeper.
OmniDiskSweeper, OmniWeb, and OmniPresence - The Omni Group

Be sure to download the correct version for the operating system you’re on. It’s free and great at finding where all large files are then lists them in order of size. I’m not sure however whether this program will analyze non Mac formatted drives. In any case, it would at least give you a good view of the Mac drive for a faster comparison to the windows drive.

There should be an explanation for the size discrepancy. If you dragged and dropped there is a possibility that some of the files failed to move although you would have gotten a message of some sort. Err on the side of caution and don’t erase the larger drive just yet.
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