The 5U NAS is a network attached Storage server. Basically, one can load as many drives as possible (20 in this case), and combined the storage space into one massive drive. There are safety measures to take in place to assure that data loss is minimal. In this instance, the 20 drives will only have 18 used for storage calculation. Therefore, if each drive is an 12TB drive, then the server will show itself as a 216TB drive.
The 5U server can be essential for either a media server, or a NAS server. A media server will hold all of the video content, music. There will be a Linux app that will be designed to allow the media server to connect with the media player, and recognize the server for files. However, the big goal is for content of videos such as TV shows, or movies. One could for example buy a movie, and download it to the media server. This will then store the movie, and if the internet goes down for whatever the reason, then the owner can watch the movies on the media server.
A NAS (Network Attached Storage) server is intended to provide a resource for hosting less used but essential files, as well as act like a backup. Many experts recommend having a backup system that is 4 times the capacity of the drive. This means a 128GB storage should have 512GB of backup storage. It is not recommended to plug in external drives to the server. This is because if the external hard drive fails, then you lose that content. If a single drive fails in a NAS server, then the system has backup of your backup in place. It will mark that drive as dead, and send a message to the owner that the particular drive is dead. This will give time for the owner to buy a new drive, and allow the server to rebuild the drive’s content.