Design a file system.

When designing a file system, focus on the core functionalities such as data storage, retrieval, and organization. Consider the structure of directories and files, including how to manage metadata and permissions. Discuss the choice between different types of file systems (e.g., FAT, NTFS, ext4) and their trade-offs in terms of performance, scalability, and fault tolerance. Address how you would handle concurrency, data integrity, and recovery in case of failures. Be prepared to explain your design decisions and how they impact user experience and system performance.