Disk I/O limits the performance of file systems on modern computers. While the cost of disk reads can be lowered by caching and prefetching, disk writes are harder to optimize. Writes can be delayed and reordered up to a point, but this is limited by the need to maintain file system integrity. The result is frequent use of small, synchronous writes.

This paper presents a scheduling and layout algorithm to maximize disk write bandwidth and improve reliability in a file system with commodity disks. Our algorithm delays and schedules all writes while maintaining system integrity. We do this with a novel combination of segment layout, lazy allocation, request sorting/coalescing, phase-specific recovery.

We have implemented a prototype of our file system on Pentium PCs running Windows NT 4.0 and have compared its performance with NTFS running on the same hardware. Our system outperforms NTFS by a factor of 2 to 10 for writing in I/O intensive benchmarks, while offering comparable read bandwidth.

Dates of work:
November 1997 - February 2000