File System Implementation

• File-System Structure
• File-System Operations
• Directory Implementation
• Allocation Methods
• Free-Space Management
• Efficiency and Performance

1. Why a file system is organized in layers?

• Minimize the duplication of code
• File system organized into layers
• Each layer in the design uses the features of lower layers to create new features.

2. What are two categories of structures used in file system implementation?

• On-disk (on-storage) structures
• In-memory structures

3. What is File Control Block or inode?

• Each file has a File Control Block or inode

4. What open file tables are there in an operating system? What are they used for?

• Search the directory structure on disk for the file and copy the content of entry （metadata） to system-wide open file table if the file is opened for the first time

• Update the per-process open-file table by adding a pointer to system-wide open file table

5. What methods are used to allocate disk blocks to files？

• Contiguous allocation(not common now)
• Linked allocation (e.g. FAT32 in Windows)
• Indexed allocation (e.g. ex3 in Unix)

6. What are main methods used to manage free space on disk?

• Bit Map
• Linked List
• Grouping
• Counting