Expandable NAS are network storage devices without pre-installed hard drives. The advantage is that you decide how much storage space you need, and quickly replace disks to increase capacity. Expandable NAS often have 2, 4 or more hard drive bays. This allows you to run RAID setups, with which you can store films, series, photos and documents in a secure manner to prevent data loss or damage. Expandable NAS are available in models that stream HD or 4K footage, make multiple backups of different computers, and run virtual machines. As a result, an expandable NAS requires a more advanced installation than ready-to-use network drives.