Chapter 01: Character of Distributed Systems 1 Distributed Computing.
Unit-IV Distributed Computing Systems Distributed Computing models Issues in designing...
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Transcript of Unit-IV Distributed Computing Systems Distributed Computing models Issues in designing...
Unit-IV Distributed Computing Systems Distributed Computing models Issues in designing distributed
operating systems DCE
Computer Architecture Multiprocessors Types
• Tightly Coupled Multiprocessor System (Parallel )
Computer Architecture Multiprocessors Types
• Loosely Coupled Multiprocessor System(Distributed )
Parallel v/s Distributed Systems
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Parallel Systems Distributed Systems
Memory Tightly coupled shared memoryUMA, NUMA
Distributed memoryMessage passing, RPC, and/or used of distributed shared memory
Control Global clock controlSIMD, MIMD
No global clock controlSynchronization algorithms needed
Processor interconnection
Order of TbpsBus, mesh, tree, mesh of tree, and hypercube (-related) network
Order of GbpsEthernet(bus), token ring and SCI (ring), myrinet(switching network)
Main focus PerformanceScientific computing
Performance(cost and scalability)Reliability/availabilityInformation/resource sharing
What is a distributed system?
• Tanenbaum’s definition of a distributed system: “A distributed system is a collection of independent computers that appear to the users of the system as a single coherent system.”
An example of a Distributed System
• Nationalized Bank with multiple Branch Offices
Requirements of Distributed systems
• Security and reliability.• Consistency of replicated data.• Concurrent transactions (operations which
involve accounts in different banks; simultaneous access from several users, etc)
• Fault tolerance
What is a Distributed Computing System?
• "a collection of processors interconnected by a communication network in which each processor has its own local memory and other peripherals and the communication between any two processors of the system takes place by message passing over the communication network" (Sinha97)
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Evaluation of Distributed Computing System
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1945-1950s Loading monitor
1950s-1960s Batch system
1960s Multiprogramming
1960s-1970s Time sharing systems Multics, IBM360
1969-1973 WAN and LAN ARPAnet, Ethernet
1960s-early1980s
Minicomputers PDP, VAX
Early 1980s Workstations Alto
1980s – present
Workstation/Server models
Sprite, V-system
1990s Clusters Beowulf
Late 1990s Grid computing Globus, Legion
Distributed Computing System Models
• Minicomputer model• Workstation model• Workstation-server model• Processor-pool model• Cluster model• Grid computing
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Minicomputer Model
• Extension of Time sharing system– User must log on his/her home minicomputer.– Thereafter, he/she can log on a remote machine by telnet.
• Resource sharing– Database– High-performance devices
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Mini-computer
Mini-computer
Mini-computer
ARPAnet
Workstation Model
• Process migration– Users first log on his/her personal workstation.– If there are idle remote workstations, a heavy job may migrate to
one of them.• Problems:
– How to find an idle workstation?– How to migrate a job?– What if a user log on the remote machine?
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100MbpsLAN
Workstation
Workstation Workstation
WorkstationWorkstation
Workstation-Server Model
• Client workstations– Diskless– Graphic/interactive applications processed in local– All file, print, http and even cycle computation
requests are sent to servers.• Server minicomputers
– Each minicomputer is dedicated to one or more different types of services (print, database,…etc).
• Client-Server model of communication– RPC (Remote Procedure Call)– RMI (Remote Method Invocation)
• A Client process calls a server process’ function.• No process migration invoked• Example: NFS
• Disadvantage : capability of idle workstations is not utilized. 13
100GbpsLAN
Workstation
Workstation Workstation
Mini-Computerfile server
Mini-Computerhttp server
Mini-Computer
print server
Processor-Pool Model
• Clients:– They log in one of terminals (diskless
workstations or X terminals)– All services are dispatched to
servers.• Servers:
– Necessary number of processors are allocated to each user from the pool.
• Better utilization but less interactivity
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Server 1
100MbpsLAN
Server N
Cluster Model
• Client– Takes a client-server model
• Server– Consists of many
PC/workstations connected to a high-speed network.
– Puts more focus on performance: serves for requests in parallel.
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100MbpsLAN
Workstation
Workstation Workstation
Masternode
Slave1
SlaveN
Slave2
1Gbps SAN
http server1
http server2
http server N
Grid Computing
• Goal– Collect computing power of supercomputers
and clusters sparsely located over the nation and make it available as if it were the electric grid
• Distributed Supercomputing– Very large problems needing lots of CPU,
memory, etc.• High-Throughput Computing
– Harnessing many idle resources• On-Demand Computing
– Remote resources integrated with local computation
• Data-intensive Computing– Using distributed data
• Collaborative Computing– Support communication among multiple parties
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High-speedInformation high way
Super-computer
Cluster
Super-computer Cluster
Mini-computer
Workstation
Workstation Workstation
Why are Distributed Computing Systems Gaining Popularity?
• Inherently distributed applications– Distributed DB, worldwide airline reservation, banking system
• Information sharing among distributed users– CSCW (Computer Supported Cooperative Works )or groupware
• Resource sharing– Sharing DB/expensive hardware and controlling remote lab. devices
• Better cost-performance ratio / Performance– Emergence of Gbit network and high-speed/cheap MPUs– Effective for coarse-grained or embarrassingly parallel applications
• Reliability– Non-stopping (availability) and voting features.
• Scalability, Extensibility and Incremental Growth– Loosely coupled connection and hot plug-in
• Flexibility– Reconfigure the system to meet users’ requirements
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Distributed Computing Environment (DCE)
What is DCE?DCE ArchitectureDCE Components
DCE • Vendor Independent Environment • Defined by OSF a consortium of computer manufacturers .• Nither OS or an application ,integrated set of services • software that supplies a framework and toolkit for developing
client/server applications• The framework includes a Remote Procedure Call (RPC) mechanism, a naming (directory) service, a time service, authentication service, authorization service Distributed File System.
Distributed Computing Environment
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Platforms
Threads
Distributed File Service
RPC
Security
Name
Distributed Time Service
DCE Applications
DCE
• Support the development of distributed application in a single system
• Platform independent ,runs on all OS and heterogeneous DS
• Middle ware software between OS and networking layer and DCE applications layer.
• Hides the difference between machines by automatically performing data type conversion
DCE Architecture
DCE(Components ) • Fundamental distributed services provide tools for software developers to
create the end-user services needed for distributed computing. They include
– Remote Procedure Call, which provides portability, network independence, and secure distributed applications.
– Directory services, which provides a single naming model to allow programmers and maintainers to identify and access distributed resources more easily.
– Time service, which provides a mechanism to monitor and track clocks in a distributed environment and accurate time stamps to reduce the load on system administrator.
– Security service, which provides the network with authentication, authorization, and user account management services to maintain the integrity, privacy, and authenticity of the distributed system.
– Thread service, which provides a simple, portable, programming model for building concurrent applications.
DCE • Data-sharing services provide end users with capabilities built
upon the fundamental distributed services. These services require no programming on the part of the end user and facilitate better use of information. They include
– Distributed file system, which interoperates with the network file system to provide a high-performance, scalable, and secure file access system.
– Diskless support, which allows low-cost workstations to use disks on servers, possibly reducing the need/cost for local disks, and provides performance enhancements to reduce network overhead.
DCE components
DCE Cell Largest management unit in DCE is cell.(group of users, machines
and other resources) The highest privileges within a cell are assigned to a role called
cell administrator Breakdown a large system into small ,manageable units called cell.
Major components of DCE within every cell are:
– The security server that is responsible for authentication
– The Cell Directory Server (CDS) that is the repository of resources and Access Control Lists
– The Distributed Time Server that provides an accurate clock for proper functioning of the entire cell.
DCECell • Setting up a DCE system ,decide cell boundaries • Four factors1. Purpose :users and m/c’s with same task must be
put in same cells.2. Administration: to register new users in the
system.3. Security : machines of those users have trust in
each other put in same cell4. Overhead : m/c’s of users frequently interacting
put in same cell