File Systems

By the end, you can

• Describe what a raw disk provides and why a file system is necessary.
• Identify the five on-disk regions and explain each one's role.
• List what an inode stores and explain why the file name is absent.
• Explain how a directory maps names to inodes and why that makes renaming cheap.
• Trace the step-by-step path resolution for an absolute path like /home/ada/notes.txt.
• Explain why a file's blocks are scattered and how the inode's pointers restore order.
• Compare contiguous, linked/FAT, and indexed allocation by their access speed and fragmentation properties.
• Describe the direct, single-indirect, double-indirect, and triple-indirect pointer tiers and the file size each covers.
• Explain how a free-space bitmap works and what bit values mean.
• Distinguish internal fragmentation from external fragmentation.
• Contrast hard links and symbolic links in terms of inode sharing, link count, cross-filesystem capability, and dangling behavior.
• Trace the three-step journal write cycle (log, commit, check-point) and explain crash recovery.
• Distinguish ext4's three journaling modes by what each logs and its safety/speed trade-off.
• Explain what the VFS is and why programs can use the same system calls across different filesystem types.