Scan-Based Scheduling and Layout in a Reliable Write-Optimized File System

Abstract:

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