MSC class devices - thumbdrives - should work. Many posters here have had success with USB connected hard-drives. I don't have a tested limit to give you, unfortunately.
Just bought the above TV and am very pleased with it but I'm having great difficulty finding out the maximum USB stick size I can use for the media player.
Any help gratefully received as the Samsung web site is a nightmare to navigate and I've failed to find any relevant information.
Thanks in advance.