17: Distributed File Systems 1 Jerry Breecher OPERATING SYSTEMS Distributed File Systems.
Distributed systems-A Brief Introduction
Transcript of Distributed systems-A Brief Introduction
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Distributed Systems
A Brief Introduction
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OUTLINE BRIEF HISTORY.
WHAT ARE DISTRIBUTED SYSTEMS ?
? WHY DISTRIBUTED SYSTEMS ? ?
ADVANTAGES OF D.S. OVER THE
CENTRALIZED SYSTEM. ADVANTAGES OF D.S. OVER
INDEPENDENT PCS.
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OUTLINE (Contd.) ORGANISATION OF DISTRIBUTED
SYSTEM.
GOALS OF D.S.
Resource Sharing.
Openness.
Transparency.
Scalability.
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OUTLINE (Contd.) Concurrency.
TYPES OF DISTRIBUTED SYSTEMS.
Distributed Computing Systems.
Distributed Information Systems.
Distributed Pervasive Systems. SUMMARY.
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HISTORY 1945~1985
Computers were large and expensive.
No way to connect them.
All systems were Centralized Systems.
Mid-1980s
Powerful microprocessors.
High Speed Computer Networks (LANs , WANs).
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HISTORY (Contd.)
Then came the
DISTRIBUTED
SYSTEMS
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What are Distributed Systems ? ?
A distributed system is a piece of software that
ensures that: a collection ofindependent computers appears
to its users as a single coherent system.
Two aspects:
(1) independent computers and (2) single
system => middleware.
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EXAMPLES World Wide Web (WWW) is the biggest
example of distributed system.
Others are
The internet
An intranet which is a portion of the internet
managed by an organization
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WHY DISTRIBUTED
SYSTEMS ? ?
availability of powerful yet cheap
microprocessors (PCs, workstations),
continuing advances in communication
technology
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ADVANTAGES OF D.S. OVER
CENTRALIZED SYSTEM: Economics:
A collection of microprocessors offer a better
price/performance than mainframes. Low
price/performance ratio: cost effective way to
increase computing power.
Reliability:
If one machine crashes, the system as a whole
can still survive. Higher availability and
improved reliability.
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ADVANTAGES (Contd.)
Speed: a distributed system may have more
total computing power than a mainframe.
Ex.: 10,000 CPU chips, each running at 50
MIPS. Not possible to build 500,000 MIPS
single processor.
Enhanced performance through loaddistributing.
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ADVANTAGES (Contd.)
Incremental growth: Computing power
can be added in small increments. This
leads to Modular expandability
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ADVANTAGES OF D.S. OVER
INDEPENDENT PCs:
Data sharing: allow many users to access
to a common data base.
Resource Sharing: expensive peripherals
like color printers.
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ADVANTAGES (Contd.)
Communication: enhance human-to-
human communication. E.g.: email, chat.
Flexibility: spread the workload over the
available machines
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ORGANIZATION OF D.S.:
A distributed system organized as middleware.
The middleware layer extends over multiple machines, and offers each
application the same interface.
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GOALS OF D.S. :
Resource Sharing.
Openness.
Transparency.
Scalability.
Concurrency.
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RESOURCESHARING: With Distributed Systems, it is easier for users to
access remote resources and to share resourceswith other users.
Examples: printers, files, Web pages, etc
A distributed system should also make it easier forusers to exchange information.
Easier resource and data exchange could causesecurity problemsa distributed system shoulddeal with this problem.
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OPENNESS:
The openness of DS is determined primarily
by the degree to which new resource-
sharing services can be added and be madeavailable for use by a variety of client
programs.
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TRANSPARENCY:
It hides the fact that the processes and
resources are physically distributed across
multiple computers.
Transparency is of various forms as
follows:
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TRANSPARENCY (Contd.)
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SCALABILITY:
A system is described as scalable if it
remains effective when there is a significant
increase in the number of resources and thenumber of users.
Challenges:
Controlling the cost of resources or money.
Controlling the performance loss.
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CONCURRENCY:
There is a possibility that several clients
will attempt to access a shared resource at
the same time.
Any object that represents a shared resource
in a distributed system must be responsible
for ensuring that operates correctly in aconcurrent environment.
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TYPES OF D.S. :
Distributed Computing Systems.
Cluster Computing Systems.
Grid Computing Systems.
Distributed Information Systems.
Distributed Pervasive Systems.
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DISTRIBUTED COMPUTING
SYSTEMS:
Goal: High performance computing tasks.
Cluster Computing Systems:
A supercomputer built from off the
shelf computer in a high-speed network
(usually a LAN)
Most common use: a single program is run
in parallel on multiple machines
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(Contd.)
Grid Computing Systems:
Contrary to clusters, grids are usually
composed of different types of computers
(hardware, OS, network, security, etc.)
Resources from different organizations are
brought together to allow collaboration
Examples: SETI@home, WWW
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DISTRIBUTED
INFORMATION SYSTEMS:
Goal: Distribute information across severalServers.
Remote processes called Clients access theservers to manipulate the information
Different communication models are used.
The most usual are RPC (Remote ProcedureCalls) and the object oriented RMI (RemoteMethod Invocations)
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(Contd.)
Often associated with Transaction systems
Examples:
Banks;
Travel agencies;
Rent-a-Cars; Etc
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DISTRIBUTED PERVASIVE
SYSTEMS:
These are the distributed systems involving mobile
and embedded computer devices like Small,
wireless, battery-powered devices (PDAs, smartphones, sensors, wireless surveillance cams,
portable ECG monitors, etc.)
These systems characterized by their instability
when compared to more traditional distributedsystems
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(Contd.)
Pervasive Systems are all around us, and ideallyshould be able to adapt to the lack of humanadministrative control:
Automatically connect to a different network;
Discover services and react accordingly;
Automatic self configuration (E.g.: UPnP
Universal Plug and Play) Examples: Home Systems, Electronic Health
Care Systems, Sensor Networks, etc.
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SUMMARY
Distributed systems are everywhere
Internet, intranet, wireless networks.
Resource sharing is the main motivating
factor for constructing distributed systems.
The construction of distributed systems
produces many challenges like Securecommunication over public networks.