In many cases we may wish to use iTunes as our media interface, especially if we use an add on program to help iTunes sound good such as, Bit Perfect, Amarra, Pure Music, Audirvana. And when using iTunes as the media organizer for ur library, we may also wish to store our media on an external hard drive.
iTunes allows users to choose where their music libraries are located: either locally or over a network. By default, iTunes stores music and media on the computer’s main internal hard drive, in a folder labeled iTunes. If you wish to change this location it is easy.
Open iTunes->Preferences->Advanced to see the location of the iTunes library. You may select Change if you wish to use an external hard drive or NAS. You must first make sure the desired drive is attached and recognized by your computer. Once you select this drive, all music that iTunes manages will be accessed on this drive.
You will also note there is a checkbox that allows for iTunes to always copy any new additions to the iTunes to this location or not.