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
Structural changes, such as le creation and block allocation, have consistently been identied 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: