My understanding is this: the itunes library is a database and it has a path for each song. The path tells it which folder it is in - or which folder within a folder within a folder. As long as all your "moving operations" are within itunes, the itune libary keeps track of where each file is. It is the library that contains the tag, not the actual song. Itunes links the tag in the library with the path of the song to keep a tag associated with a song.
If you are using an external hard drive for your original ripped music files, great. All you need to do is make a duplicate copy of that hard drive - meaning preserving the folder structure - on your backup hard drive. You might call your primary hard driver "Music-1" and your backup hard drive "Music-2". If Music-1 ever crashed, you could just rename Music-2 to Music-1, and itunes wouldn't know the difference. It would still be looking at an external hard drive called (renamed) Music-1, and all the music files would be in place within the exact same folder structure, because you carefully made sure that the two hard drives had the same folder structures. However, if yu let itunes move things around on Music-1 without making the same structural changes on Music-2, the paths in the library would not correspond to Music-2, and if Music-1 went down, itunes would no longer be able to associate the defunct paths to songs with the tags.
You should also backup your library file, along with your music files. You can do it somewhere on Music-2.