With Traktor Scratch Pro 2 there's an option to Auto Analyze with the launch of software. It does this with external hard drives as well just as long as you have the file path saved for import. Each subfolder does not have to be saved, just the single parent folder or name of the external device. I really think this would be a great option for Serato DJ instead of having to drag folders/files. Traktor does this for auto BPM calculations as well.