merging 3 external hard drives without duplicated

yardenacoca

Prominent
Sep 27, 2017
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Hi everybody,
My grandpa has 3 external hard drives which were permanent backup over the past few years. The data is mostly photos, videos and documents. He bought a new larger hard drive, to include all his data from those old 3. Problem is - in those 3, there's a lot(!) of duplicates.
any idea on how to merge them all easily and create only one non-duplicates hard drive to contain it all?

thanks in advance,
Jordan.