Btrfs Copy-on-Write File System

Btrfs (B-tree file system) is a modern copy-on-write file system for Linux that provides advanced features including subvolumes, snapshots, compression, deduplication, and built-in RAID. Initially developed at Oracle by Chris Mason in 2007, with contributions from Facebook, SUSE, Red Hat, and the Linux community, Btrfs is the default filesystem on SUSE Linux Enterprise Server, Fedora, and Synology NAS devices. Key features include: copy-on-write (COW architecture ensures modifications create new data extents rather than modifying existing ones, enabling atomic updates and crash recovery without journal replay), subvolumes (independent filesystem trees within a single Btrfs partition, each with its own root directory, mountable independently with per-subvolume quotas and compression), snapshots (instant read-only or read-write copies of subvolumes for backup, rollback, and testing, created by duplicating the root tree pointer without copying data), compression (ZSTD, LZO, and zlib transparent compression with per-file and per-subvolume configuration), checksumming (CRC32C or XXHash3 checksums on all data and metadata blocks with automatic detection of silent data corruption), self-healing (when combined with RAID or device mirror, corrupted data is automatically repaired from redundant copies during read), RAID support (native software RAID levels 0, 1, 10, 5, and 6 with per-extent balancing and restriping for online RAID level conversion), send and receive (incremental and full subvolume replication for backup and disaster recovery), deduplication (out-of-band deduplication via duperemove for eliminating duplicate data extents), online resize (grow and shrink filesystems without unmounting), free space tree (improved free space tracking for better performance), and Linux mainline (fully integrated into the Linux kernel since 2009).