Transcript Distributed Systems Architecture

Distributed Systems
Architecture
Presenters
Rose Kit & Turgut Tezir
Outline
Introduction to Distributed System
Characteristics of Distributed System
Advantages of Distributed System
Disadvantages of Distributed System
Loosely-coupled Systems
Tightly-coupled system
Array Processor
Introduction to Distributed System
Centralized System
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A single computer with one ore more CPUs processes all incoming
request
Problems with cost, reliability
Specification and implementation are defined within a single
system
Distributed System
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Opposite of centralized system
Set of separate computers that are capable of autonomous
operation, link by a compute network.
Enable individual computers (different location) to share resources
in the network
Server implementation for the same interface located in different
servers.
Distributed and Centralized Computer
System
Characteristics of Distributed System
Resource sharing
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Resource provided by a computer which is a member of a
distributed system can be shared by clients and other members
of the system via a network.
“Resource Manager” is a software module (based on set of
management policies) that provides interfaces which enables
resource to be manipulated by clients, Openness
Openness
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Resource sharing services can be incorporated without
disruption or duplication of existing services
Concurrency
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All concurrent access must be synchronised to avoid problems
such as lost update, dirty read, incorrect summary &
unrepeatable read.
Characteristics of Distributed System
Scalability
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flexible to grow in size.
Fault tolerance
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the system appropriately handles errors
hardware redundancy, software recovery
Transparency
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hide all unnecessary details from users
Example: Location transparency - clients do not need to know
the location of the servers
Advantages of Distributed System
Shareability
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Allows systems to use each other’s resources
Expandability
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Permits new systems to be added as members of the overall
system
Local Autonomy
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Manage local resources
Improved performance
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Resource replication
Combined processing power of multiple computers provides
much more processing power than a centralised system with
multiple CPUs
Improved reliability and availability
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disruption would not stop the whole system from providing its
services as resources spread across multiple computers
Potential cost reductions
Disadvantages of Distributed System
Network reliance
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problems on network would disrupt activities in the system as a
whole
Complexities
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must be able to deal with errors from all computers that make up
the distributed system
Security
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private resources would be exposed to a wider range of potential
hackers, with unauthorised accesses from any computers
connected to the system
centralised system is more secure
General Types of Distributed Systems
Loosely-Coupled Systems
Tightly-Coupled Systems
Array Processor Systems
Loosely-coupled Systems
Loosely-coupled distributed systems are single-user computers or
workstations that are locally networked enabling them to access
shared data and resources located in other server computers
Most distributed systems links two types of computers, workstations
and servers (also known as client/server).
An early example of the client/server model is the Xerox distributed
system
Systems with different hardware and software can be networked
together
Advantages of loosely coupled systems over tightly coupled
systems:
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More scalable.
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Generally more reliable/fault-tolerant.
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Allows sharing of widely separated resources.
Loosely-coupled Systems
A Loosely-coupled System
Local Network
Memory
Memory
Memory
Memory
Prg A
Prg B
Prg C
Prg D
Processor
Processor
Processor
Processor
I/O
I/O
I/O
I/O
Tightly-coupled system
Tightly-coupled system connects a number of processor into an
integrated hardware system under the control of a single operating
system.
The operating system assigns processor and memory space to
users’ tasks and allow them to run at the same time.
The hardware environment includes a shared memory or a highspeed connection between several separate processor / memory
systems with a unified virtual addressing system. This enables
users’ tasks to communicate with each other and with the operating
system.
Advantage of tightly coupled systems over loosely coupled systems:
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Easier to program but expensive (Limited by the memory
bandwidth)
A Tightly-coupled Multiprocessor
System
Shared Memory
Program A
Program B
Program C
Program D
Cache
Memory
Cache
Memory
Cache
Memory
Cache
Memory
Processor
Processor
Processor
Processor
Input / Output
Array Processor
An array processor is similar to a personal computer with a large
number of arithmetic and logic units linked in a regular array. They
can be used to perform operations in parallel on arrays of data.
The distinguishing characteristics of such a machines is that the
entire array of processors obeys a single stream of instructions,
some of the instructions being applied to many data items
distributed throughout the array of processing unit.
There are also other tightly–coupled distributed systems that are
designed to make calculations faster by processing them in parallel.
Advantages:
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Useful for achieving high processing speed when processing
large regular set of data
Disadvantages
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Geographical distribution
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Many independent tasks need to executed at the same time.
Array Processor
M
M
M
M
M
M
M
M
M
P
P
P
P
P
P
P
P
P
Program
Input / Output
M: Memory
P: Processor