UFS2

UFS2 is the second version of the Unix File System (UFS), a file system developed for BSD-derived operating systems. It was designed to replace UFS1 in these systems, offering greater scalability and reliability for modern storage devices. UFS2 introduced 64-bit addressing for both file offsets and disk blocks, enabling support for very large files and storage volumes. The on-disk layout was extended to increase maximum filesystem sizes and to reduce metadata contention through more robust allocation strategies. It also improved timestamp precision and metadata integrity, providing better support for sub-second timestamps and crash recovery. In addition, UFS2 added support for extended attributes and POSIX ACLs in many implementations, as well as optional quotas at the filesystem level.

As an implementation detail, UFS2 maintains multiple copies of important metadata and uses a structure of inodes, directories, and blocks designed for efficient streaming access. It is supported by BSD family operating systems such as FreeBSD and DragonFly BSD, and is often the default filesystem on those platforms or offered alongside UFS1. Converting or migrating an existing UFS1 filesystem to UFS2 typically requires tooling and kernel support, and may involve data backup and restore.

UFS2 is distinct from other BSD filesystems (such as ZFS on some systems) in being block-oriented, simpler, and historically easier to recover in certain failure conditions, though it lacks some advanced features of newer filesystems.