week12_friday - CSCC 69H3 Operating Systems Spring 2010...

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CSCC 69H3 Operating Systems Spring 2010 Professor Bianca Schroeder U of T
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Today: Distributed file systems
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3/29/2005 CSC369 What is a Distributed System? “You know you have one when the crash of a computer you’ve never heard of stops you from getting any work done.” - Leslie Lamport, 1987 A collection of (perhaps) heterogeneous nodes connected by one or more interconnection networks which provides access to system-wide shared resources and services. A collection of independent computers that appears to its users as a single coherent system.
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3/29/2005 CSC369 Key Features Multiple computers May be heterogenous, or homogeneous May be controlled by a single organization or by distinct organizations or individuals Connected by a communication network Typically a general-purpose network, not dedicated to supporting the distributed system Co-operating to share resources and services Application processing occurs on more than one machine
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3/29/2005 CSC369 Technology Trends Parallel processing - divide computation among multiple physical processors 2 schemes for building such systems multiprocessor system: tightly coupled; the processors share memory and a clock; communication usually takes place through shared memory; dedicated internal communication network distributed system: loosely coupled; processors do not share memory or a clock; communication usually takes place through external general-purpose networks Cheap, powerful desktop computers High performance networks
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3/29/2005 CSC369 Motivation for Dist. Systems Resource sharing Computation speedup can allow subcomputations to be run concurrently load sharing Reliability if enough redundancy exists, the system can continue operation, even with some sites failing Communication support for group collaboration applications Network
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3/29/2005 CSC369 Terminology From the viewpoint of a specific processor in a Distributed System, the rest of the processors and their resources are remote , and its own are local Computing entities in the DS are referred to by many names sites , nodes, computers, machines, hosts ,… Network P1 P2
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3/29/2005 CSC369 Operating System Options Network OS Each computer has its own private OS OS includes network services to allow access to remote resources User is aware of multiple computers and must deal with them explicitly. Distributed OS
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week12_friday - CSCC 69H3 Operating Systems Spring 2010...

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