The file system likely has a POSIX like-or-unlike filesystem interface. Because it is meant to be used directly by unmodified programs on the platforms the file

The file system likely has a POSIX like-or-unlike filesystem interface. Because it is meant to be used directly by unmodified programs on the platforms the file system is supported on as the file system is accessible via the operating system's virtual filesystem interface. The storage system might not. It might be like those online storage systems from A&G that only support put and get and have to be used via specific access libraries. (Although someone might make a virtual filesystem interface to them.)