Bcachefs

Bcachefs is a copy-on-write (COW) file system for Linux-based operating systems.[5] Features include caching,[6] full file-system encryption using the ChaCha20 and Poly1305 algorithms,[7] native compression[6] via LZ4, gzip[8] and Zstandard,[9] snapshots,[6] CRC-32C and 64-bit checksumming.[5] It can span block devices, including in RAID configurations.[7]

Earlier versions of Bcachefs provided all the functionality of Bcache, a block-layer cache system for Linux, with which Bcachefs shares about 80% of its code.[1] As of December 2021, the block-layer cache functionality has been removed.[9]

On a data structure level, bcachefs uses B-trees like many other modern file systems, but with an unusually large node size defaulting to 256 KiB. These nodes are internally log-structured, forming a hybrid data structure, reducing the need for rewriting nodes on update.[10] Snapshots are not implemented by cloning a COW tree, but by adding a version number to filesystem objects.[11] The COW feature and the bucket allocator enables a RAID implementation with neither write hole nor IO fragmentation.[9]

Primary development has been by Kent Overstreet, the developer of Bcache, which he describes as a "prototype" for the ideas that became Bcachefs. Overstreet intends Bcachefs to replace Bcache.[1] Overstreet has stated that development of Bcachefs began as Bcache's developers realized that its codebase had "been evolving ... into a full blown, general-purpose POSIX filesystem", and that "there was a really clean and elegant design" within it if they took it in that direction. Some time after Bcache was merged in 2013 into the mainline Linux kernel, Overstreet left his job at Google to work full-time on Bcachefs.[5]

After a few years' unfunded development, Overstreet announced Bcachefs in 2015, at which point he called the code "more or less feature complete", and called for testers and contributors. He intended it to be an advanced file system with modern features[12] like those of ZFS or Btrfs, with the speed and performance of file systems such as ext4 and XFS.[5] As of 2017 Overstreet was receiving financial support for the development of Bcachefs via Patreon.[7]

As of mid-2018, the on-disk format had settled.[1] Patches had been submitted for review to have Bcachefs included in the mainline Linux kernel, but had not yet been accepted.[6]

By mid-2019, the desired features of Bcachefs were completed and the associated patches to LKML were submitted for peer review.[2][3] In September 2023 the filesystem was merged in linux-next, a development tree of the Linux kernel where new features are tested before inclusion in the mainline tree.[13]

• Official website