University of Michigan Technical Report CSE-TR-254-95, August 1995.

Soft Updates: A Solution to the Metadata Update Problem in File Systems

Gregory R. Ganger, Yale N. Patt

Department of Electrical Engineering and Computer Science
The University of Michigan, Ann Arbor 48109-2122


Structural changes, such as le creation and block allocation, have consistently been identi ed as a source of problems (performance, integrity, security and availability) for le systems. This report describes soft updates, an implementation technique that allows a le system to safely use delayed writes for metadata updates. We show that a le system using soft updates asymp- totically approaches memory-based le system performance while providing stronger integrity and security guarantees than most UNIX le systems. For metadata update intensive benchmarks, this improves performance bymore than a factor of two when compared to the conventional synchronous write approach. In addition, soft updates can improve le system availability by relegating crash-recovery assistance (e.g., the fsck utility) to an optional and/or background role, reducing le system recovery time to a few seconds.

This report, which describes soft updates in general and our implementation in detail, is broken into two files to simplify on-line access:

Available Online