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1、VirtualizationinLinuxKirillKolyshkinSeptember1,2006AbstractThreemainvirtualizationapproaches—emulation,paravirtualiza-tion,andoperatingsystem-levelvirtualization—arecovered,followedbytheimplementationexamples,comparisonofthetechnologiesand
2、theirapplications.OS-levelvirtualizationisdescribedindetail,withexamplesfromOpenVZ.Themainkernelcomponents(isolationandvirtualization,resourcemanagement,checkpointingandlivemigra-tion)anduser-leveltoolsarealsoexplained.Typicalusagescenariosofvirtualizatio
3、nsolutionsarepresented.1Virtualization.Typesofvirtualization.Inthecontextofthisreport,virtualizationisasystemoramethodofdividingcomputerresourcesintomultipleisolatedenvironments.Itispossibletodistinguishfourtypesofsuchvirtualization:emulation,paravirtuali
4、zation,operatingsystem-levelvirtualization,andmultiserver(cluster)virtualization.Thelastapproachisoutofscopeofthisreport.Eachvirtualizationtypehasitsprosandconsthatconditionitsappro-priateapplications.Emulationmakesitpossibletorunanynon-modifiedoperatingsy
5、stemwhichsupportstheplatformbeingemulated.Implementationsinthiscat-egoryrangefrompureemulators(likeBochs)tosolutionswhichletsomecodetobeexecutedontheCPUnatively,inordertoincreaseperformance.Themaindisadvantagesofemulationarelowperformanceandlowdensity.Exa
6、mples:VMwareproducts,QEmu,Bochs,Parallels.ParavirtualizationisatechniquetorunmultiplemodifiedOSsontopofathinlayercalledahypervisor,orvirtualmachinemonitor.Paravirtual-izationhasbetterperformancecomparedtoemulation,butthedisadvantageisthatthe“guest”OSneedst
7、obemodified.Examples:Xen,UML.1Operatingsystem-levelvirtualizationenablesmultipleisolatedex-ecutionenvironmentswithinasingleoperatingsystemkernel.Ithasthebestpossible(i.e.closetonative)performanceanddensity,andfeaturesdynamicresourcemanagement.Ontheotherhan
8、d,thistechnologydoesnotallowtorundifferentkernelsfromdifferentOSsatthesametime.Exam-ples:FreeBSDJail,SolarisZones/Containers,Linux-VServer,OpenVZandVirtuozzo.2ConceptofaVEVirtualEnvironment(VE,alsoknownasVPS,container
