The Ongoing BcacheFS Filesystem Stability Controversy

In a saga that brings to mind the hype and incidents with ReiserFS, [SavvyNik] takes us through the latest data corruption bug report and developer updates regarding the BcacheFS filesystem …read more

Jun 10, 2025 - 12:20

The Ongoing BcacheFS Filesystem Stability Controversy

In a saga that brings to mind the hype and incidents with ReiserFS, [SavvyNik] takes us through the latest data corruption bug report and developer updates regarding the BcacheFS filesystem in the Linux kernel. Based on the bcache (block cache) cache mechanism in the Linux kernel, its author [Kent Overstreet] developed it into what is now known as BcacheFS, with it being announced in 2015 and subsequently merged into the Linux kernel (6.7) in early 2024. As a modern copy-on-write (COW) filesystem along the lines of ZFS and btfs, it was supposed to compete directly with these filesystems.

Despite this, it has become clear that BcacheFS is rather unstable, with frequent and extensive patches being submitted to the point where [Linus Torvalds] in August of last year pushed back against it, as well as expressing regret for merging BcacheFS into mainline Linux. As covered in the video, [Kent] has pushed users reporting issues to upgrade to the latest Linux kernel to get critical fixes, which really reinforces the notion that BcacheFS is at best an experimental Alpha-level filesystem implementation and should probably not be used with important data or systems.

Although one can speculate on the reasons for BcacheFS spiraling out of control like this, ultimately if you want a reliable COW filesystem in Linux, you are best off using btrfs or ZFS. Of course, regardless of which filesystem you use, always make multiple backups, test them regularly and stay away from shiny new things on production systems.