Yes, you can turn your external hard disk into a NAS. I know, we want to access our content from anywhere, but we don't have a NAS. There are several apps that can help to turn your external hard disk into a NAS. However, you will need to have at least 4TB of storage on your hard disk for it to give you the best storage. The apps include QNAP and Drive among others. These apps allow you to create a private cloud on any external hard disk without having to spend money on a dedicated device for this purpose.