Filesystems

How data is organized and persisted on storage

The filesystem stack

Application: open("/data/file", O_RDONLY)
          │
          ▼
     VFS layer            ← generic operations (see vfs/)
          │
          ▼
  Filesystem driver       ← ext4, btrfs, xfs, tmpfs, ...
          │
          ▼
     Page cache           ← in-memory cache of disk blocks
          │
          ▼
   Block layer (bio)      ← submits I/O to disk
          │
          ▼
    Block device          ← NVMe, SATA, virtio-blk

Pages in this section

Page	What it covers
ext4	On-disk layout, extents, journaling with jbd2
tmpfs and ramfs	Memory-backed filesystems, size limits
btrfs	Copy-on-Write B-tree, subvolumes, snapshots

Choosing a filesystem

Filesystem	Use case	Key feature
ext4	General purpose, servers	Stable, journaled
btrfs	Desktop, NAS	CoW, snapshots, RAID
xfs	High-performance servers	High scalability
tmpfs	/tmp, /run, shared memory	RAM-backed, fast
overlayfs	Container images	Union of layers
squashfs	Read-only (LiveCD, containers)	Compressed, read-only
erofs	Android, embedded	Compressed, fast read