Abstracts for Papers Published by the Ficus Project
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Name Transparency in Very Large Scale Distributed File
Systems.
Previous distributed file systems have relied on either
convention or obtaining dynamic global agreement to provide
network transparent file naming. This paper argues that
neither approach can succeed as systems scale to the kind of
size that is anticipated in the current decade. We propose
instead a novel name mapping scheme which relies on a
fragemented, selectively replicated name translation database.
Updates to the naming database are coordinated by an
optimistic concurrency control strategy with automatic
propagation and reconciliation. A prototype of the name
mapping mechanism has been implemented and is in use in the
Ficus replicated file system. Available at
file://ftp.cs.ucla.edu/pub/ficus/ExpDistSys_90.ps.gz
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An Analysis of Trace Data for Predictive File Caching
in Mobile Computing.
One way to provide mobile computers with access to the
resources of a network, even in the absence of communication,
is to predict which information will be used during
disconnection and cache the appropriate data while still
connected. To determine the feasibility of this approach,
traces of file-access activity for three diverse application
domains were collected for periods of over two months.
Analysis of these traces using traditional and new measures
reveals that user working sets tend to be small compared to
modern disk sizes, that users tend to reference the same files
for several days or even weeks at a time, and that different
users do not tend to write to the same file except in highly
constrained circumstances. These factors encourage the
conclusion that an automated caching system can be built for a
wide variety of environments.
Available via ftp.
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Resolving File Conflicts in the Ficus File System
.
Ficus is a flexible replication facility with optimistic concurrency
control designed to span a wide range of scales and network
environments. Optimistic concurrency control provides rapid local
access and high availability of files for update in the face of
disconnection, at the cost of occasional conflicts
that are only discovered when the system is reconnected.
Ficus reliably detects all possible conflicts. Many conflicts can be
automatically resolved by recognizing the file type
and understanding the file's semantics. This paper describes
experiences with conflicts and automatic conflict resolution in Ficus.
It presents data on the frequency and character of conflicts in our
environment. This paper also describes how semantically knowledgeable
resolvers are designed and implemented, and discusses our experiences
with their strengths and limitations. We conclude from our experience
that optimistic concurrency works well in at least one realistic
environment, conflicts are rare, and a large proportion of those conflicts
that do occur can be automatically solved without human intervention.
Available via ftp.
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Security Issues in the Truffles File System
.
Truffles is a system meant to address some of the major
issues that still make it difficult to share files between users
at different sites. In particular, it addresses the problems
associated with secure file sharing, and the problems of high
administrative overhead. Truffles will combine facilities of
the Ficus file system and TIS/PEM, a privacy enhanced mail
ssytem, to make file sharing consideably easier. Truffles
must deal with several important security problems,
including secure transport of data, authentication of the users
sharing files, handling of different administrative domains,
and permitting system administrators to control, flexibly,
yet easily, what sorts of sharing are done. This paper
describes these problems and the solutions Truffles will use.
Not yet available via ftp.
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Truffles - Secure File Sharing With Minimal System
Administrator Intervention
.
The Truffles file system supports file sharing between arbitrary
users at arbitrary sites connected by a network. Truffles is an
interesting example of a service of the future that will automatically
allow users to collaborate with other users anywhere in the world in
ways not currently possible. These services, and Truffles in
particular, have the potential of greatly increasing the workload
of system administrators, if the services are not designed properly.
This paper describes how Truffles approaches solving its problems
without unduly burdening system administrators.
Not yet available via ftp.
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The Design of the SEER Predictive Caching System.
Supporting portable computers in a disconnected environment
will require persistent caching of files without user
intervention. SEER is a system that uses semantic information
to predict which files the user is likely to work on, and
arranges to transparently cache them on the portable platform
prior to disconnection. We present the overall design of the
SEER system and the algorithms used to determine semantic
relationships.
Available via ftp.