Metadata Update Performance in File Systems

Structural changes, such as file creation and block allocation, have consistently been identified as file system performance problems in many user environments. We compare several implementations that maintain metadata integrity in the event of a system failure but do not require changes to the on-disk structures. In one set of schemes, the file system uses asynchronous writes and passes ordering requirements to the disk scheduler. These scheduler-enforced ordering schemes outperform the conventional approach (synchronous writes) by more than 30 percent for metadata update intensive benchmarks, but are suboptimal mainly due to their inability to safely use delayed writes when ordering is required. We therefore introduce soft updates, an implementation that asymptotically approaches memory-based file system performance (within 5 percent) while providing stronger integrity and security guarantees than most UNIX file systems. For metadata update in- tensive benchmarks, this improves performance by more than a factor of two when compared to the conventional approach.