Introduction

BTRFS is a modern copy on write (COW) filesystem for Linux aimed at implementing advanced features while also focusing on fault tolerance, repair and easy administration. Its main features and benefits are:

Snapshots which do not make a full copy of the files
Built-in volume management, support for software-based RAID 0, RAID 1, RAID 10 and others
Self-healing - checksums for data and metadata, automatic detection of silent data corruptions
Data compression
Reflinks, fast and efficient file copies

Feature overview

Extent based file storage
2⁶⁴ byte (16 EiB) maximum file size (practical limit is 8 EiB due to Linux VFS)
Space-efficient packing of small files
Space-efficient indexed directories
Dynamic inode allocation
Writable snapshots, read-only snapshots, subvolumes (separate internal filesystem roots)
Checksums on data and metadata (crc32c, xxhash, sha256, blake2b)
Compression (ZLIB, LZO, ZSTD), heuristics
Integrated multiple device support:
- File Striping (like RAID0)
- File Mirroring (like RAID1 up to 4 copies)
- File Striping+Mirroring (like RAID10)
- Single and Dual Parity implementations (like RAID5/6, experimental, not production-ready)
SSD/NVMe (flash storage) awareness, TRIM/Discard for reporting free blocks for reuse and optimizations (e.g. avoiding unnecessary seek optimizations, sending writes in clusters.
Background scrub process for finding and repairing errors of files with redundant copies
Online filesystem defragmentation
Offline filesystem check
In-place conversion of existing ext2/3/4 and reiserfs filesystems
Seeding device. Create a (readonly) filesystem that acts as a template to seed other Btrfs filesystems. The original filesystem and devices are included as a readonly starting point for the new filesystem. Using copy on write, all modifications are stored on different devices; the original is unchanged.
Subvolume-aware quota support
Send/receive of subvolume changes, efficient incremental filesystem mirroring and backup
Batch, or out-of-band deduplication (happens after writes, not during)
Swapfile support
Tree-checker, post-read and pre-write metadata verification
Zoned mode support (SMR/ZBC/ZNS friendly allocation, emulated on non-zoned devices)

A more detailed list of features and compatibility is on the status page.

Quick start

For a really quick start you can simply create and mount the filesystem. Make sure that the block device you’d like to use is suitable so you don’t overwrite existing data.

# mkfs.btrfs /dev/sdx
# mount /dev/sdx /mnt/test

The default options should be acceptable for most users and sometimes can be changed later. The example above is for a single device filesystem, creating a single profile for data (no redundant copies of the blocks), and DUP for metadata (each block is duplicated).