Phase 4 — File Systems (Weeks 13–16). Read the original FFS, LFS, and ext4 papers directly — the textbook summaries lose the insight. Pay special attention to journaling and crash consistency because it connects back to Phase 2's atomicity concepts.
As you go along, you need to finish the following topics:
File System Abstractions
Inodes and Directory Structure
FAT, ext4, NTFS — FS Internals
Block Allocation — Bitmaps and Free Lists
Journaling and Write-Ahead Logging
Log-Structured File Systems
Caching — Buffer Cache and Page Cache
File System Consistency and fsck
RAID — Redundancy and Performance
Network File Systems — NFS, SMB
Flash Storage and Log-Structured Merge Trees
VFS — Virtual File System Layer