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Comparing Filesystems: ext4 vs XFS vs Btrfs vs ZFS

Introduction​

When you create a filesystem on top of a logical disk, you’re not just choosing how data is stored — you’re also choosing how failures are handled, how metadata is structured, and how well the system scales. In this article, we’ll compare four of the most commonly used Linux filesystems: ext4, XFS, Btrfs, and ZFS.

ext4: The Workhorse​

  • Journaling: Metadata journaling with optional data journaling mode. Keeps recovery simple and fast after crashes.
  • Extents: Introduced to reduce fragmentation by grouping contiguous blocks together.
  • Overhead: Minimal compared to copy-on-write systems. Metadata and journal add some fixed cost.
  • Crash Consistency: Strong, as journal replay restores metadata to a consistent state.
  • Use Case: Default choice for general-purpose Linux installs. Reliable, stable, well-tested.

XFS: Scaling for Large Systems​

  • Journaling: Metadata journaling, optimized for parallel I/O.
  • Extent Strategy: Uses delayed allocation and B+ trees to manage large files efficiently.
  • Metadata Overhead: Heavier than ext4, but scales better for very large volumes.
  • Crash Consistency: Journal ensures metadata integrity, but not data blocks themselves.
  • Use Case: Enterprise workloads with multi-terabyte filesystems and high concurrency.

Btrfs: The Experimenter’s Playground​

  • Copy-on-Write (CoW): Instead of overwriting, new blocks are allocated and old ones are freed later. This improves crash safety but increases write amplification.
  • Snapshots & Subvolumes: Built-in support for snapshots, rollback, and lightweight clones.
  • Metadata Overhead: Higher than ext4/XFS due to checksumming and CoW duplication.
  • Crash Consistency: Strong due to CoW — old data is preserved until new writes succeed.
  • Use Case: Advanced users needing snapshots, built-in RAID, or self-healing via checksums.

ZFS: The Tank​

  • Copy-on-Write: Like Btrfs, but more mature and integrated with end-to-end checksumming.
  • Advanced Features: Built-in compression, deduplication, RAID-Z, and snapshots.
  • Extent/Block Strategy: Transaction groups aggregate writes before committing, ensuring consistency.
  • Metadata Overhead: High; ZFS reserves significant memory and CPU for ARC (cache) and metadata operations.
  • Crash Consistency: Very strong — transactional semantics ensure atomicity.
  • Use Case: Enterprise storage, large datasets, situations where data integrity is paramount.

Journaling vs Copy-on-Write​

  • Journaling: Write twice (data + journal), then replay journal after crash. Faster recovery, but risk of partial data loss if crash occurs between data and metadata commits.
  • Copy-on-Write: Write new blocks, update metadata atomically. Guarantees consistency at the cost of higher write amplification and fragmentation.

Extents, Metadata, and Overhead​

  • ext4/XFS: Use extents and journaling, aiming for efficiency and speed.
  • Btrfs/ZFS: Use CoW with checksumming, snapshots, and extra features, but incur more overhead.

Crash Consistency in Practice​

  • ext4/XFS: Journals ensure you don’t lose filesystem structure, but recent writes may vanish.
  • Btrfs/ZFS: Old data remains valid until new writes are fully committed. Safer, but slower in some workloads.

Conclusion​

There is no “one best filesystem.”

  • Choose ext4 if you want stability and simplicity.
  • Choose XFS for scaling large filesystems.
  • Choose Btrfs if you want CoW features like snapshots.
  • Choose ZFS if your priority is maximum data integrity and enterprise-grade features.

Your logical disk may be the same, but the filesystem you put on top will shape your performance, reliability, and capabilities.