How to compare files/folders on two different disks

a program like carbon copy cloner or super duper can some times copy a drive that disk utility can not. Last time I used super duper, it told me what file it couldn't copy.

the terminal "sudo ditto -v /copy/this/folder/ /copy/folder/to/here/" will copy a folder, and give you a message for any file or folder it could not copy.

the terminal command "diff -rq /path/to/original/ /path/to/copy" will tell you what files & folders are different.

personally, I avoid using diff. I use ditto to copy.
the reason why is ditto is detecting when a file fails to transfer, at the time of transfer. diff on the other hand is comparing the files after the fact.
Plus I would expect less missing files by coping the folders using ditto. See if your dragging a folder, and it fails mid copy, the copy stops. If your using ditto, ditto skips the file it could not copy. then it tells you it couldn't copy that file, and then continues on.

Dragging a folder will cause the copy to have new ownership settings. While ditto tries to keep the ownership of the files intact.

I hope this helps.

good luck 😀