USENIX Symposium on Operating Systems Design and Implementation, November, 1994, pp. 4960.
Metadata Update Performance in File Systems
Gregory R. Ganger, Yale N. Patt
Department of EECS
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 ondisk structures. In one set of schemes, the file system uses asynchronous writes and passes ordering requirements to the disk scheduler. These schedulerenforced 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 memorybased file system performance (within 5 percent) while providing stronger integrity and security guarantees than most UNIX file systems. For metadata update intensive benchmarks, this improves performance by more than a factor of two when compared to the conventional approach.