Automated Hoarding for Mobile Computers

A common problem facing mobile computing is disconnected operation, or computing in the absence of a network. Hoarding eases disconnected operation by selecting a subset of the user's files for local storage. We describe a hoarding system that can operate without user intervention, by observing user activity and predicting future needs. The system calculates a new measure, semantic distance, between individual files, and uses this to feed a clustering algorithm that chooses which files should be hoarded. A separate replication system manages the actual transport of data; any of a number of replication systems may be used. We discuss practical problems encountered in the real world and present usage statistics showing that our system outperforms previous approaches by factors that can exceed 10:1. 1 Introduction The face of computing today is rapidly being changed by the advent of mobility, but the utility of the portable computer is seriously challenged by the problem of disconnect..

Abstract To appear, ACM Transactions on Computer Systems. File System Development with Stackable Layers

Filing services have experienced a number of innovations in recent years, but many of these promising ideas have failed to enter into broad use. One reason is that current ling environments present several barriers to new development. For example, le systems today typically stand alone instead of building on the work of others, and support of new ling services often requires changes which invalidate existing work. Stackable le system design addresses these issues in several ways. Complex ling services are constructed from layer \building blocks", each of which may be provided by independent parties. There are no syntactic constraints to layer order, and layers can occupy di erent address spaces, allowing very exible layer con guration. Independent layer evolution and development is supported by an extensible interface bounding each layer. This paper discusses stackable layering in detail and presents design techniques it enables. We describe an implementation providing these facilities that exhibits very high performance. By lowering barriers to new ling design, stackable layering o ers the potential of broad third party le system development not feasible today. This work was sponsored by the Defense Advanced Research Projects Agency under contracts F29601-87-C-0072 and N00174-91-C-0107. Also, John Heidemann was sponsored by a USENIX scholarship for the 1990-91 academic year, and Gerald Popek is a liated with Locus Computing Corporation

A Layered Approach to File System Development

This paper discusses the stackable layers approach to file system design. With this approach, a file system is constructed from several layers, each implementing one portion of the file system well. Each layer is bounded above and below by an identical interface framework. The symmetry of the interface, coupled with run-time stack definition, make layer configuration flexible and facilitate experimentation and new file system development. Addition of new file system functionality to existing environments often requires changes to current interfaces. To address this issue, stackable layers are joined by an extensible interface. Any layer can add to such an interface; existing layers continue to function without modification. Stackable architectures benefit from new development techniques. This paper examines development methods unique to stackable systems, and concludes with an analysis of the performance of layered file systems. 1 Introduction The utility of modular structures in s..