The Ratings, Genre and some other metadata are store in the iTunes library.itl file
You can move to another drive, then update the Media location in preference.
Read this Article for Moving
You must tick Consolidate Files, as in step 10.
In the library folder, you will see exclamation marks on all your songs, indicating missing file,
but just click on the first one, click locate.
Then iTunes will ask you if you want to locate the rest - > click ok.