distributedsystems-13 - Distributed Systems-1 A Distributed...

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-1 Distributed Systems 
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-2 A Distributed System
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-3 Loosely Coupled Distributed Systems Users are aware of multiplicity of machines.  Access to  resources of various machines is done explicitly by: Remote logging into the appropriate remote machine. Transferring data from remote machines to local machines, via  the File Transfer Protocol (FTP) mechanism.
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-4 Tightly Coupled Distributed-Systems Users not aware of multiplicity of machines.  Access to  remote resources similar to access to local resources Examples Data Migration – transfer data by transferring entire file, or  transferring only those portions of the file necessary for the  immediate task. Computation Migration – transfer the computation, rather  than the data, across the system.
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-5 Distributed-Operating Systems (Cont.) Process Migration – execute an entire process, or parts of it, at  different sites. Load balancing – distribute processes across network to even the  workload. Computation speedup – subprocesses can run concurrently on different  sites. Hardware preference – process execution may require specialized  processor. Software preference – required software may be available at only a  particular site. Data access – run process remotely, rather than transfer all data locally.
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-6 Why Distributed Systems? Communication Dealt with this when we talked about networks Resource sharing Computational speedup Reliability
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-7 Resource Sharing Distributed Systems offer access to specialized resources  of many systems Example: Some nodes may have special databases Some nodes may have access to special hardware devices (e.g. tape  drives, printers, etc.) DS offers benefits of locating processing near data or  sharing special devices 
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-8 OS Support for resource sharing Resource Management? Distributed OS can manage diverse resources of nodes in system Make resources visible on all nodes  Like VM, can provide functional illusion but rarely hide the  performance cost Scheduling? Distributed OS could schedule processes to run near the needed  resources If need to access data in a large database may be easier to ship  code there and results back than to request data be shipped to  code
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-9 Design Issues   Transparency  – the distributed system should appear as a  conventional, centralized system to the user.
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