In the world of Linux filesystems, finding the perfect balance between performance and advanced features has long been a challenge. Traditional workhorses such as ext4 and XFS deliver speed and stability but lack modern capabilities, whereas feature-rich alternatives such as Btrfs and ZFS come with complexity and caveats. Bcachefs [1] – merged into the Linux kernel 6.7 – promises the best of both worlds, aiming to marry the reliability and powerful features of ZFS/Btrfs with the efficiency of ext4/XFS. Bcachefs is a copy-on-write (CoW) filesystem designed for robustness without sacrificing speed. The bcachefs filesystem offers native support for checksumming, compression, encryption, snapshots, tiered storage, and multi-device configurations, all the while delivering consistent low-latency performance and robust data integrity.

Bcachefs developer Kent Overstreet has had some high-profile battles with Linus Torvalds, and the status of future kernel support keeps changing depending on who you talk to and when you talk to them. Linus has stated that the kernel will be "parting ways" with bcachefs in version 6.17 [2]. As of this writing, though, bcachefs is included in the current Linux kernel, and support could continue if the antagonists resolve their differences. Whether or not bcachefs continues as an active part of the kernel, it is still worth a look as an example of how the world of the Linux filesystem keeps evolving.

Architecture and Features

Bcachefs was built from the ground up to be a next-generation CoW filesystem that won't eat your data. Its core design inherits concepts from the earlier bcache block-layer cache, with which it originally shared much code, evolving that prototype into a full POSIX-compatible filesystem. Bcachefs uses CoW semantics similar to Btrfs and ZFS – data and metadata are never overwritten in place, enabling atomic updates and consistent snapshots. All modifications are written to new locations, which not only facilitates reliability but also allows features such as snapshotting and reflinking (efficiently copying or cloning files) by design.

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