was added on linux 6.7 # Under the hood first announced in 2015, BcacheFS is based on Bcache([the work on that was started 2010](https://en.wikipedia.org/wiki/Bcache) and ended up getting him a job at google to work on it). The goal of bcache was to use the speed of an SSD as a cache for a bigger HDD while keeping in mind the performance and restriction of both. bcache was describe by its main dev Kent Overstreet as a prototype for bcachefs, in fact in 2018, [80% of bcachefs code was shared with on bcache](https://lwn.net/Articles/755276/) BcacheFS is, just like [[BTRFS]], making use of a B+ Tree which can be **roughly** summarize as a binary tree that can hold more than 2 leaves [VISUALIZE HERE](https://www.cs.usfca.edu/~galles/visualization/BPlusTree.html) Inside of each node is a large (256K) log structure, so you can ensure fast write by only having to append nodes in case of a change instead of a complete rewrite. [SOURCE](https://bcachefs.org/Architecture/#Btree_internals.3A) The big superpower of the FS is the power of hindsight, Kent was able to sidestep most issues that plagues other FS like ZFS and BTRFS as he was able to engineer his FS with those problem in mind from the start. # Feature ## Copy on write (COW) do not overwrite only write the changes to the data, redirect on write insult.... also support - Nocow mode ## Snapshot Snapshot are implemented differently than other CoW system, instead of copying the B Tree, it adds version key ,also called snapshot id, to FS item (inodes, dirents, xattrs, extents). ## Reflink The ability to have 2 file with the same root data ## Multiple devices and replication You can use Bcache with multiple drive at a time, have some redundancy and even set a specific job for each drive: bcachefs format \ --label=ssd.ssd1 /dev/sdA \ --label=ssd.ssd2 /dev/sdB \ --label=hdd.hdd1 /dev/sdC \ --label=hdd.hdd2 /dev/sdD \ --label=hdd.hdd3 /dev/sdE \ --label=hdd.hdd4 /dev/sdF \ --replicas=2 \ --foreground_target=ssd \ --promote_target=ssd \ --background_target=hdd the replicas command can give you something akin to Raid 1 or Raid10 depending on how many drive you feed into the FS ## Full data and metadata checksumming Ensuring that corruption are detected ## Compression gzip, lz4, and zstd ## Encryption AEAD style encryption (ChaCha20/Poly1305) ## more STD things that all FS have: ## Xattr Extended file attributes are additional attributes that only apply to specific file like copyright name or date a picture was taken. ## ACL Access Control Lists is, as the name implies, a list of permission added to the main perm, help do fine tuning of the permission of a file in a complex environment. ## Quotas BcacheFS has what we call user/group/project quotas, a project id can be assign to any Dir and will be enforced recursively # Unfinished feature ## Erasure coding / Raid 5&6 the ability to make Raid 5/6 style config, meaning having parity stripped across all of your drive is still in the works, remember BTRFS, it is a big problem for those type of FS [MEGA SOURCE](https://bcachefs.org/) # Terms Stripes: Bcachefs stripes data by default, similar to RAID0. Redundancy is handled via the **replicas** option. 2 drives with `--replicas=2` is equivalent to RAID1, 4 drives with `--replicas=2` is equivalent to RAID10, etc. [Bcachefs - ArchWiki (archlinux.org)](https://wiki.archlinux.org/title/Bcachefs) Dirty: What isn't yet saved into permanent storage, isn't the same as cache but don't know why.... Disk accounting: The collection of size (meta)data on stored file # History BEFORE: argument with linux about norms with Kent [Re: [GIT PULL] bcachefs - Linus Torvalds (kernel.org)](https://lore.kernel.org/lkml/CAHk-=wjUX287gJCKDXUY02Wpot1n0VkjQk-PmDOmrsrEfwPfPg@mail.gmail.com/) ## Linux 6.7: Got into the kernel ## Linux 6.11: Conversion to the "New" Mounting API. [[General Functions#"New" mounting API]] Better lockdep coverage (Lockdep is a tool) [[General Functions#Lockdep]] Self healing on read IO/checksum error data is now automatically rewritten **if we get a read error and then a** **successful retry** Disk accounting rewrite Older Disk accounting wasn't scalable, now it is. We now have counters for compression type/ratio, per-snapshot-id usage, per-btree-id usage, and pending rebalance work. Stripe sectors accounting This is needed for ensuring that erasure coding is working correctly, as well as completing stripe creation after a crash. ^00222b [[GIT PULL] bcachefs changes for 6.11 - Kent Overstreet (kernel.org)](https://lore.kernel.org/lkml/r75jqqdjp24gikil2l26wwtxdxvqxpgfaixb2rqmuyzxnbhseq@6k34emck64hv/) adding another disk accounting counter to be used for counting disk usage and the number of extents per inode number. This "bcachefs_metadata_version_disk_accounting_inum" is needed for Bcachefs to track fragmentation. (so to implement defrag in the futur) also fixed an issue where a thread would be left running under specific circumstance. [Bcachefs Merges New On-Disk Format Version For Linux 6.11, Working Toward Defrag - Phoronix](https://www.phoronix.com/news/Bcachefs-Merge-Linux-6.11-rc4) getting in a fight with linus and violating simlpe rules of Kernel devs [Linus Torvalds Begins Expressing Regrets Merging Bcachefs - Phoronix](https://www.phoronix.com/news/Linus-Torvalds-Bcachefs-Regrets) In the benchmark BcacheFS is now only slower than BTRFS in 2 benchmark, getting better and better. [An Initial Benchmark Of Bcachefs vs. Btrfs vs. EXT4 vs. F2FS vs. XFS On Linux 6.11 - Phoronix](https://www.phoronix.com/review/linux-611-filesystems) ## Linux 6.12 Kent wants his FS to be stable next year and claims it can be 3-4x faster than XFS [Bcachefs Hopes To Remove "EXPERIMENTAL" Flag In The Next Year - Phoronix](https://www.phoronix.com/news/Bcachefs-For-Linux-6.12) linus is thinking about removing after patch leading to unbuildable kernel on big endiand machine. Lack of transparency and testing by kent and the wider community is to blame. [Bcachefs Fixes Pull Once Again Frustrates Linus Torvalds - Two Choices Offered - Phoronix](https://www.phoronix.com/news/Bcachefs-Fixes-Two-Choices) Bug reduced by 40% [Bcachefs Reining In Bugs: Test Dashboard Failures Drop By 40% Over Last Month - Phoronix](https://www.phoronix.com/news/Bcachefs-Failures-Drop-40p)