Frequent copies of large folder with sub-folders - new files only?

I regularly copy my music files to a second internal hard drive and also to a
removable Lacie. The exercise consists of a folder with a hundred or so sub
folders containing 9,000+mp3 files. Is there any way to copy only those
files which aren't already on the two backup drives? Or do I just have to
wear the 90 minutes it takes for each one to copy each file?
thanks for helping.
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Hoges in WA