DISTRIBUTED SYSTEM-A TOOL FOR BUILDING DEPENDABLE DISTRIBUTED SYSTEM

Physically, a Distributed System consists of a set of processors, with a collection
of local storage mechanisms associated with each processor. A processor is able to execute
programs that access and manipulate the local storage, where the term process denotes the
locus of control of an executing program. In addition, an interconnection network connects
the processors and allows them to communicate and share data via exchange of
messages.These messages are encapsulated inside packets when transmitted on the
network.
We conceptually view the underlying distributed system in terms of an object
model in which the system is said to consist of a collection of objects. An object is either a
physical resource, or an abstract resource. Objects are further characterized as being
either passive or active, where passive objects correspond to stored data, and active
objects correspond to processes that act on passive resources. For the purposes of this
thesis, we use the term object to denote only passive objects.
There has been very little empirical data published on file system usage or
performance. Obtaining trace data is difficult, typically requiring careful modifications to
the operating system, and the resulting data is voluminous. The published studies tend to
deal with older operating systems, and for this reason may not be applicable in planning
future systems.Our main concerns in gathering the data were the volume of the data and affecting the
results by logging them through the cache system under measurement. We wished to gather
data over several days to prevent temporary anomalies from biasing the data. The method
settled upon used the local area network to send the trace data to another system, where it
was written to magnetic tape. Logging routines inserted into the file system code placed the
trace records in a memory buffer.
This article describes the practicalities in Distributed System concept and principles and
its advancements from the earlier technologies.