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Btrfs: modern and feature-packed

Btrfs (B-tree File System) is a modern, copy-on-write (COW) file system for Linux designed to address the limitations of older file systems like Ext4. It provides advanced features such as snapshots, data integrity verification, built-in volume management, and more. Btrfs aims to combine the functionalities of traditional file systems and logical volume managers, making it a versatile and powerful tool for managing storage.

Key features of Btrfs include:

  1. Copy-on-Write (COW): Btrfs uses copy-on-write (COW) for data and metadata, meaning that when data is modified, the changes are written to new locations on disk instead of overwriting the original data. This approach ensures that the previous version of the data is preserved, which is crucial for features like snapshots and data integrity. It also makes copies of data on the same volume instantaneous, because both refer to the same block of data on disk. COW provides benefits such as atomic writes, where operations are either fully completed or not done at all, reducing the risk of data corruption.
  2. Snapshots: Snapshots are read-only or read-write copies of the file system at a specific point in time. Snapshots are efficient and fast because they share common data blocks until changes to the data on the disk are made. Snapshots are ideal for backup, system rollback, and testing purposes. They allow you to capture the state of the file system and revert back to it later if necessary. With certain system configurations it is even possible to boot into a snapshot.
  3. Data Integrity and Checksumming: Btrfs provides checksumming for both data and metadata. Every block of data and metadata is verified with a checksum when read or written. If corruption is detected (e.g. due to hardware failure), Btrfs can attempt to recover the data using its checksums. This feature significantly improves the file system's reliability, especially in environments where data integrity is critical.
  4. Built-in Volume Management: Btrfs includes volume management features natively, which means it can handle multiple physical devices and manage them as a single logical volume. This feature eliminates the need for external volume managers like LVM (Logical Volume Manager). It supports RAID-like configurations (RAID 0, RAID 1, RAID 10) natively, allowing users to create storage pools with redundancy and striping.
  5. Compression and Deduplication: Btrfs natively supports transparent compression, allowing data to be stored in a compressed format to save space. Several algorithms (such as LZO and zstd) are available for use. Deduplication (removal of duplicate data) can also be performed, making it ideal for environments with large amounts of redundant data where storage space is precious.
  6. Dynamic Sizing and Subvolumes: Btrfs allows the dynamic resizing of file systems, making it easy to increase or decrease the size of volumes as needed, without requiring reformatting or complex migrations. Subvolumes are logical divisions of a file system that can be treated like separate file systems. Each subvolume can have its own set of snapshots, making them useful for organizing data, creating backups, or managing different applications in isolation. Subvolumes can also be used to install multiple different operating systems on the same file system without getting into the way of one another.
  7. Online Defragmentation: Btrfs supports online defragmentation, meaning that it can reorganize and defragment the file system while the system is running, which can help improve performance over time, especially on systems with high churn of small files.
  8. Self-healing: In combination with its checksumming capabilities, Btrfs is able to self-heal data when used with RAID configurations. For example, in a RAID 1 setup, if one disk has corrupted data, Btrfs can detect the issue and restore the correct data from the mirrored copy.

The rich feature set of Btrfs makes it a modern and versatile choice for data storage on Linux. Built-in volume management at the file system level eliminates having to think about partition layouts and sizes, while the RAID capabilities make an underlying software RAID layer redundant. Snapshots allow for quick rollbacks to a previous state of the system without wasting precious space. Transparent compression and deduplication maximize efficient use of storage space. When used effectively, Btrfs is an excellent and future-proof choice.

However, because Btrfs is still a relatively new file system, some features are still not considered ready for daily use, e.g. integrated RAID 5/6 support currently being considered unstable. It also often ranks worse than other file systems in areas where high throughput is important, such as database applications or as backing storage for virtual machines. The complex feature set may also pose a high learning curve for people unfamiliar with its concepts.

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