Ive got a laptop with two internal hard drives, the original 300 gb hard drive and an additional 1tb hard drive that I added. The 1tb is the main storage for my image files when I copy them from the SD cards. I just discovered that about 100gb of images are duplicated on the 300gb hard drive. Does anyone know what the reason is for the duplication and if there are any settings I can change that will result in the removal or migration of the duplicate files to the 1 tb hard drive without messing up the integrity of my catalog?
When you "copy" image files from SD cards into your (larger) second drive, do you do that yourself, or do you have Lightroom Classic do that as part of its import?
If the former, one possible explanation: LrC defaults to making a Catalog in your Pictures folder. Default destination for "Copy" imports, is here too; and that is on your primary drive by default. You may have been unwittingly making copies of these photos as part of importing them, and it would be this copy that is then imported. As another possible explanation: LrC can be set to make a duplicate 'archive copy' of each image as part of its import... that is not the one which is imported.
In order to work out what is going on: your Folders panel will summarise what images are known by LrC to be stored on which drive. At the individual image level, you can right-click and choose "Show in Finder / Explorer", to inspect the disk storage location that this image is imported from. Also you can right-click and choose "Go to Folder in Library" to inspect which folder and drive location for that, is remembered by the Catalog - which can be out of step with current reality in some circumstances, for example if stuff has been moved around using the OS file manager, behind LrC's back.
Within LrC you can change the location of image files. If you have copies on both drives, to the extent the folder arrangement is consistently named and organised, chunks of the library can be re-addressed in bulk very easily. But first you do need to investigate which of these duplicated images and folders on disk are the ones imported to LrC, and which are the ones which are not. There may be a mixture, with some imported from each drive.