Download Unit-IV - unit 1

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
Parallel Systems
Distributed Systems
Memory
Tightly coupled shared memory
UMA, NUMA
Distributed memory
Message passing, RPC, and/or used
of distributed shared memory
Control
Global clock control
SIMD, MIMD
No global clock control
Synchronization algorithms needed
Processor
interconnection
Order of Tbps
Bus, mesh, tree, mesh of tree, and
hypercube (-related) network
Order of Gbps
Ethernet(bus), token ring and SCI
(ring), myrinet(switching network)
Main focus
Performance
Scientific computing
Performance(cost and scalability)
Reliability/availability
Information/resource sharing
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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
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
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Distributed Computing System Models
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Minicomputer model
Workstation model
Workstation-server model
Processor-pool model
Cluster model
Grid computing
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Minicomputer Model
Minicomputer
Minicomputer
ARPA
net
Minicomputer
• 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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Workstation Model
Workstation
Workstation
100Mbps
LAN
Workstation
Workstation
Workstation
• 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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Workstation-Server Model
•
Client workstations
– Diskless
Workstation
– Graphic/interactive applications processed in local
– All file, print, http and even cycle computation
requests are sent to servers.
Workstation
Workstation
• Server minicomputers
– Each minicomputer is dedicated to one or more
different types of services (print, database,…etc).
100Gbps
• Client-Server model of communication
LAN
– RPC (Remote Procedure Call)
– RMI (Remote Method Invocation)
• A Client process calls a server process’ function.
MiniMiniMini• No process migration invoked
Computer Computer Computer
• Example: NFS
file server http server print server
• Disadvantage : capability of idle workstations is
not utilized.
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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
100Mbps
LAN
Server 1
Server N
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Cluster Model
Workstation
Workstation
• Client
– Takes a client-server model
Workstation
• Server
– Consists of many
100Mbps
PC/workstations connected
LAN
to a high-speed network.
http server2
http server N – Puts more focus on
http server1
performance: serves for
Slave
Master Slave Slave
requests in parallel.
node
1
2
N
1Gbps SAN
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Grid Computing
•
Workstation
Supercomputer
•
Minicomputer
High-speed
Information high way
Cluster
•
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Supercomputer
Cluster
•
•
Workstation
Workstation
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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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 Architecture
DCE Components
DCE
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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
DCE Applications
Threads
RPC
Distributed Time Service
Security Distributed File Service
Name
Platforms
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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 factors
1. 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 cell
4. Overhead : m/c’s of users frequently interacting
put in same cell