A data storage apparatus with a variable computer file system is disclosed. The variable computer file system adopts the concept of a dedicated sub-file system and is activated or deactivated according to whether authentication is granted. Each dedicated sub-file system is activated or deactivated according to whether authentication is granted, and is recognized by a host computer. Deactivated dedicated sub-file systems cannot be recognized or accessed by the host computer. Accordingly, since a third party accessing the host computer cannot access a dedicated sub-file system without possessing a means for activating the dedicated sub-file system, security is greatly strengthened.