Using asynchronous writes on metadata to improve file system performance

Abstract

Due to the increasing gap between CPU and disk I/O speeds, the file system is becoming the performance bottleneck in computer system design. How to improve file system performance is increasingly important. There are two types of entities in a file system: data and metadata. Data mean the actual contents of files. Metadata include access control and other descriptive information about files. Previous research indicates that metadata writes account for 38 - 40% of disk I/O operations. These large numbers of control request I/Os are usually ignored in traditional file system study, which concentrates only on file-level access patterns. We propose the design and implementation of a metadata-ordering mechanism and its corresponding asynchronous write facility. With such a facility, we can eliminate many synchronous metadata writes, and have the flexibility of choosing a better way to update these metadata modifications to disk asynchronously. Extensive performance evaluation shows that substantial performance improvement can be achieved under various benchmarks. Some other tests are also used to demonstrate the benefits and behaviors of this approach.