Bcachefs, an Introduction/Exploration

Original Article ↗ Hacker News Discussion ↗

Bcachefs is emerging as a new copy‑on‑write Linux filesystem aiming to combine features like checksumming, snapshots, compression, encryption and flexible multi‑disk layouts in a single, in‑kernel solution. Commenters weigh it against mature alternatives such as Btrfs and ZFS, highlighting Btrfs’s long history of data‑loss incidents and complex behavior, ZFS’s strong reliability but licensing and integration hurdles, and the risks of trusting any young filesystem with critical data. Overall, bcachefs is seen as promising for the long term, but most consider it not yet ready to replace battle‑tested setups for important storage.

Overall sentiment

  • Thread centers on comparing bcachefs, btrfs, and ZFS for reliability, features, and maturity.
  • Many are excited about bcachefs as a new in-kernel COW filesystem, but most are cautious about trusting it with important data yet.

Btrfs reliability and behavior

  • Multiple anecdotes of recent btrfs data loss or unrecoverable corruption (power cuts, full filesystems, “parent transid verify failed”, USB usage causing hard freezes).
  • Others report years to a decade of trouble‑free use, including large production deployments, and argue its bad reputation lags behind current reality.
  • Common pain points:
    • Fragility when the filesystem is 100% full.
    • RAID5/6 still officially unsafe; write‑hole problems.
    • Awkward management (balance/defrag behavior, snapshot/UUID quirks, drive removal with I/O errors).
    • Performance issues for databases/VMs due to COW; NoCOW seen as a hack that disables core features.
  • RAID1 behavior and defaults are controversial: refusing to boot without all devices is seen by some as safe, by others as an availability trap.

ZFS vs btrfs

  • Several users say ZFS has never lost data for them over many years and prefer it despite kernel/module friction.
  • Others note ZFS has had serious bugs too and is not invulnerable, especially without ECC RAM.
  • ZFS is praised for: robust snapshots, send/receive, checksumming, compression, flexible datasets, and as the backbone for backup schemes.
  • Criticisms: licensing/legal uncertainty on Linux; out‑of‑tree modules; dedup is available but considered expensive; encryption has open bug tickets but also long‑term positive anecdotes.

Bcachefs: promise and current limitations

  • Recognized as very new in‑kernel; many bugfixes landed right after merge.
  • Positives: unified feature set (COW, checksums, compression, encryption, dedup, SSD caching, flexible multi‑disk, per‑file replication). Some report smooth desktop use so far.
  • Negatives/concerns:
    • At least one report of it “eating data”; others only trust it for non‑critical systems.
    • RAID5/6 / erasure coding explicitly marked “DO NOT USE YET”.
    • RAID0‑like behavior by default with multiple disks worries some.
    • Even its advocates acknowledge they still keep important data on ZFS.
  • Recent change: upcoming Linux 6.11 adds self‑healing on checksum error; there is debate about risks of self‑healing with bad RAM, and the role of ECC.

RAID, multi‑disk, and uneven‑disk setups

  • Btrfs RAID1’s ability to mirror at the chunk level across different‑sized disks is considered a killer feature for small/home setups; bcachefs offers something similar.
  • ZFS can approximate this with manually partitioned vdevs but at the cost of complexity and performance.
  • General dissatisfaction that traditional RAID and most filesystems don’t gracefully handle disks that come and go; resilvering is seen as wasteful when little has changed, though ZFS’s incremental resilver is noted as relatively fast.