Chapter 16-1 Distributed System StructuresChapter 16 Distributed System StructuresChapter ObjectivesBackgroundDistributed System StructuresMotivationFour Important Motivations for Distributed SystemsMotivation Reasons -1Motivation Reasons – 2 of 3Motivation Reasons – 3 of 3Types of Distributed Operating SystemsNetwork Operating SystemsRemote LoginRemote File TransferDaemons for telnet and ftpDistributed Operating SystemsData MigrationComputation MigrationProcess MigrationProcess Migration – a bit more===Extra Stuff===Network StructureNetwork Structure - OverviewLocal Area Networks in context of Distributed SystemsWide Area Networks in Context of Distributed SystemsSlide 26WANs - more===== UUUC ========== PPP ============ Routers ============= Pictures of Routers ======End Chapter 16.1Chapter 16-1 Distributed System Chapter 16-1 Distributed System StructuresStructures17.2Silberschatz, Galvin and Gagne ©2005Operating System ConceptsChapter 16 Distributed System StructuresChapter 16 Distributed System StructuresChapter 16.1BackgroundMotivationTypes of Distributed Operating SystemsNetwork StructureChapter 16.2Network TopologyCommunication StructureCommunication ProtocolsRobustnessDesign Issues17.3Silberschatz, Galvin and Gagne ©2005Operating System ConceptsChapter ObjectivesChapter ObjectivesTo provide a high-level overview of distributed systems and the networks that interconnect themTo discuss the general structure of distributed operating systems.17.4Silberschatz, Galvin and Gagne ©2005Operating System ConceptsBackgroundBackgroundDistributed systems - collections of processors sharing neither memory nor a clock.Each processor has its own memory, their own facilities and other resources, and they communicate with each other via local area networks or wide area networks.Systems can vary greatly in size, performance, and a host of other characteristics. A distributed file system, in contrast, is a file-service system whose users, servers, and storage devices are distributed over different nodes in a distributed system.Associated file services must be carried out across a network. In distributed file systems, we do not have a single, centralized data repository. Rather, we have many independent storage devices, each with their characteristics. Benefits of distributed systems are many and varied. These include providing user access to resources maintained ‘elsewhere.’ Of course, such power breeds complexity and a host of other issues.Ability to speedup computations either my distributing computations, providing much greater availability to data, and the potential to distribute processes themselves are among the many benefits of distributed systems. All these ‘nice’ things require dealing with many issues such as deadlock and failures that are different than those in centralized systems.17.5Silberschatz, Galvin and Gagne ©2005Operating System ConceptsDistributed System StructuresDistributed System StructuresHere in this chapter, we will discuss many of the general issues and communication issues that support distributed systems.Clearly communication is ‘a’ key and we will talk a lot about this in this chapter. It is part and parcel to understanding the immense issues kand complexity of distributed systems.We discuss a very general structure of a distributed system (in this chapter) and the networks needed for interconnection.We will also talk about the main differences in OS design between distributed systems and centralized systems.17.6Silberschatz, Galvin and Gagne ©2005Operating System ConceptsMotivationMotivationIn distributed systems we have a collection of loosely coupled processors interconnected by a communications network.From the view of a local user, all other processors appear to be remote.Nodews on a network may be referred to as nodes, sites, computers, machines, hosts, etc. We will say site to indicate the location of a machine and host to refer to a specific system at a site. Generally one host at some site, the server, has a resource that a host at some other site, a client, wants to use.It is as simple as this – at least conceptually.17.7Silberschatz, Galvin and Gagne ©2005Operating System ConceptsFour Important Motivations for Distributed Four Important Motivations for Distributed SystemsSystemsMotivation for distributed systems are plentiful. Here are four.Resource SharingComputation SpeedupReliability, andCommunications.Each of these are very important.17.8Silberschatz, Galvin and Gagne ©2005Operating System ConceptsMotivation Reasons -1Motivation Reasons -1Resource SharingResource sharing refers to the ability to access resource(s) at a remote site, whether it is a processor, processes, printers, files, etc.Of course, many mechanisms, safeguards, and communications must be in place. We will discuss these ahead.Computation SpeedupSome operations may be broken down into different run units that might be able to be run independently. In this case, they can be run concurrently – indeed simultaneously on a number of sites at the same time.Another example of computational speedup is simply moving a job to another site because of overloading at the resident site and running that process desired at a remote site which might have system availability.Sometimes this is called load sharing.17.9Silberschatz, Galvin and Gagne ©2005Operating System ConceptsMotivation Reasons – 2 of 3Motivation Reasons – 2 of 3ReliabilityIf computers in a distributed system are somewhat general-purpose, such that the failure of one will not necessarily affect others, then similar sites may continue to run when one node goes down. If machines are special purpose or if the system consists of a number of small machines where each has some special roles in the overall system, then there may be a problem unless there is sufficient redundancy to continue.Of course, if a failure occurs, the system must be able to recover in some way.A specific faulty system must be taken out and its functionality must be transferrable to another node in the system, if we wish to maintain the same degree of ‘robustness’ that the distributed network offers..When repairs are made, then this node must be able to be brought back into the system with minimal disruption.17.10Silberschatz, Galvin and Gagne ©2005Operating