CMU-CS-02-145
Computer Science Department
School of Computer Science, Carnegie Mellon University



CMU-CS-02-145

Metadata Efficiency in a Comprehensive Versioning File System

Craig A.N. Soules, Garth R. Goodson, John D. Strunk, Gregory R. Ganger

2002

CMU-CS-02-145.ps
CMU-CS-02-145.pdf

Keywords: Versioning, file system, log-structured, journal-based metadata, multiversion b-tree, comprehensive versioning


A comprehensive versioning file system creates and retains a new file version for every WRITE or other modification request. The resulting history of file modifications provides a detailed view to tools and administrators seeking to investigate a suspect system state. Conventional versioning systems do not efficiently record the many prior versions that result. In particular, the versioned metadata t hey keep consumes almost as much space as the versioned data. This paper examines two space-efficient metadata structures for versioning file systems and describes their integration into the Comprehensive Versioning File System (CVFS). Journal-based metadata encodes each metadata version into a single journal entry; CVFS uses this structure for inodes and indirect blocks, reducing the associated space requirements by 80%. Multiversion b-trees extend the per-entry key with a timestamp and keep current and historical entries in a single tree; CVFS uses this structure for directories, reducing the associated space requirements by 99%. Experiments with CVFS verify that its current-version performance is similar to that of non-versioning file systems. Although access to historical versions is slower than conventional versioning systems, checkpointing is shown to mitigate this effect.

33 pages


Return to: SCS Technical Report Collection
School of Computer Science homepage

This page maintained by reports@cs.cmu.edu