Synthetic Files: Enabling Low-latency File I/O for QoS-Adaptive Applications

Files are a tried and true operating system abstraction. They present a simple byte-stream model of I/O that has proven intuitive for application programmers and efficient for operating system builders. However, current file systems do not provide good support for adaptive continuous media (CM) applications – an increasingly important class of applications that exhibit complex access patterns and are particularly sensitive to variations in I/O performance. To address these problems we propose synthetic files. Synthetic files are specialized views of underlying regular files, and convert complex file access patterns into simple sequential synthetic file access patterns. Synthetic file construction can be viewed as a declarative meta-interface for I/O, enabling application-driven prefetching strategies that can hide device access latency even for applications with complex access patterns. Synthetic files can be realized dynamically, incrementally, or even optimistically. In this paper we outline a feedback-driven, incremental creation strategy that hides variations in device access latency for QoS-adaptive CM applications. This project was supported in part by DARPA contracts/grants N66001-97-C-8522, N66001-97-C-8523, and F19628-95-C-0193, and by Tektronix, Inc. and Intel Corporation.