AdvFS

AdvFS, also known as Tru64 UNIX Advanced File System, is a file system developed in the late 1980s to mid-1990s^[1] 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 GNU GPL license.^[2]

Its features include:

• a journal to allow for fast crash recovery
• undeletion support
• high performance
• dynamic structure that allows an administrator to manage the file system on the fly
• on the fly creation of snapshots
• defragmentation while the domain has active users

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.

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.

AdvFS was developed by DEC engineers in Bellevue, WA (DECwest) that had previously worked on the earlier (cancelled) Mica and Ozix projects there. It was first delivered on the DEC OSF/1 system. Over time, development moved to teams located in Bellevue, WA and Nashua, NH. Versions were always one version number behind the operating system version. Thus, DEC OSF/1 v3.2 had AdvFS v2.x, Digital UNIX 4.0 had AdvFS v3.x and Tru64 UNIX 5.x had AdvFS v4.x. It is generally considered that only AdvFS v4 had matured to production level stability, with a sufficient set of tools to get administrators out of any kind of trouble. The original team had enough confidence in its log based recovery to release it without an "fsck" style recovery utility on the assumption that the file system journal would always be allocated on mirrored drives.

On June 23, 2008, its source code was released^[2] under GNU General Public License version 2 at SourceForge in order to be compatible with the Linux kernel license.

References

External links

• Source code