All of your cameras are constantly recording 24/7 and storing footage to their own internal memory (128 GB of space) for 45 days on the camera itself.  Once their storage is full, the cameras will start recording over their oldest stored footage. The amount of time and footage stored per camera is entirely based on the resolution of the camera and the amount of movement that is recorded (i.e. a higher resolution setting on the camera will take up more space, and thus store less footage internally).

There is also a 2-year cloud storage using Amazon Web Services that is strictly for "Saved Clips" and does not affect the storage function stated above.