AdvFS, also known as Tru64 UNIX Advanced File System, is a file system developed in the late 1980s to mid-1990s by Digital Equipment Corporation for their OSF/1 version of the Unix operating system (later Digital UNIX/Tru64 UNIX). In June 2008, it was released as free software under the GPL-2.0-only license. AdvFS has been used in high-availability systems where fast recovery from downtime is essential.

AdvFS uses a relatively advanced concept of a storage pool (called a file domain) and of logical file systems (called file sets). A file domain is composed of any number of block devices, which could be partitions, LVM or LSM devices. A file set is a logical file system created in a single file domain. Administrators can add or remove volumes from an active file domain, providing that there is enough space on the remaining file domain, in case of removal. This was one of the trickier original features to implement because all data or metadata residing on the disk being removed had to first be migrated, online, to other disks, prior to removal.

File sets can be balanced, meaning that file content of file sets be balanced across physical volumes. Particular files in a file set can be striped across available volumes.

Administrators can take a snapshot (or clone) of any active or inactive file set. This allows for easy on-line backups and editing.

Another feature allows administrators to add or remove block devices from a file domain, while the file domain has active users. This add/remove feature allows migration to larger devices or migration from potentially failing hardware without a system shutdown.

Its features include:

Under Linux, AdvFS supports an additional ‘’syncv’’ system call to atomically commit changes to multiple files.

AdvFS, also known as Tru64 UNIX Advanced File System, was developed by Digital Equipment Corporation engineers beginning in the late 1980s in Bellevue, WA (DECwest). It started out as the filesystem of the canceled OZIX operating system project.