If you have a large iTunes library, you may have reached the point where you need to offload some of your media files to another drive. There are several ways you can do this. You can connect an external hard drive to your Mac, and use that to store your iTunes Media folder. If you use an iMac, this is probably the easiest choice. However, if you use a laptop, you may not want the hassle of connecting and disconnecting an external drive whenever you want to use iTunes.
Another option is to use a network attached storage device, or NAS. This is a storage device that your Mac connects to over your network—usually via Wi-Fi, but you can also use Ethernet—and that can give you vastly more storage, especially if your Mac has an internal SSD.
Read more here:: How to set up an iTunes library on a network-attached server