subvolume
also: subvol
A Btrfs filesystem subdivision that acts as an independent mountable filesystem with its own namespace, snapshots, and quotas, while sharing physical storage with its parent volume.
A subvolume is a Btrfs-specific feature that partitions a single Btrfs filesystem into logically separate trees. Each subvolume can be mounted independently at different mount points, has its own inode namespace, and can be managed with distinct permissions and quotas.
Subvolumes enable efficient storage organization without the overhead of creating separate partitions. For example, on a single Btrfs filesystem you might create subvolumes for /@ (root), /@home (home directories), and /@snapshots (backups), then mount each at /, /home, and /.snapshots respectively.
Key advantages include the ability to take independent snapshots of each subvolume, apply different compression or caching settings, enforce separate disk quotas, and exclude specific subvolumes from snapshots. This makes subvolumes particularly useful for system backups and managing multi-tenant storage.