In Part 3 of our series, we explored the hardware device elements of the Reolink RLC-810A ― focusing on the NAND memory. We continue with Part 4 of our exploration into an IP camera firmware through introducing the concept of a file system. Furthermore, we will explore the technical reasons for choosing the UBI File System (UBIFS), a file system used especially for a category of mass storage, and we will unpack the UBIFS part using the ubi-extract tool.