中科院高能物理研究所计算中心 范勇

AFS--AndrewFileSystem中科院高能物理研究所计算中心范勇2002.11.11内容安排AFS概述AFS的组成与功能AFS管理AFS应用===================AFS概述AFSisanenterprisefilesystemdesignedforuseinadistributedenvironmentonmultiplecomputingplatforms.AFS的发展历史AFS分布式文件系统计算环境AFS分布式文件系统计算环境AFS的特性Asingle,sharednamespaceforallusers,fromallmachines.Location-independentfilesharing.Clientcachingandefficientwide-areaprotocolsforexcellentperformanceExtendedsecuritythroughKerberosauthenticationandAccessControlListsReplicationtechniquesforfilesystemreliabilityAFS中的几个基本概念CellVolumesMountPointsReplicationCachingandCallbacksTokensAccessControlListCellAcellisanindependentlyadministeredsiterunningAFS.Amachinecanonlybelongtoonecellatatime.Usersalsobelongtoacellinthesenseofhavinganaccountinit,butunlikemachinescanbelongto(haveanaccountin)multiplecells./usr/vice/etc/CellDB/usr/afs/etc/CellDBVolumesAnAFSvolumeisalogicalunitofdiskspacethatfunctionslikeacontainerforthefilesinanAFSdirectory,keepingthemalltogetherononepartitionofafileservermachine.Makeadministrativetaskseasierandhelpimproveoverallsystemperformance.ThreetypesofvolumesinAFS:–singleread/writeversion–read-onlyvolume–backupvolumeMountPointsMechanismthatassociatesthedirectoryandvolumeiscalledamountpoint.MountPoints==========VolumesReplicationReplicationreferstomakingacopy,orclone,ofasourceread/writevolumeandthenplacingthecopyononeormoreadditionalfileservermachinesinacell.Increasestheavailabilityofthecontents.Mostappropriateforvolumesthatcontainpopularfilesthatdonotchangeveryoften.Caching&CallbacksTheproblemofmaintainingconsistencyamongthemanycachedcopiesofafileandthesourceversionofafile.AcallbackisapromisebyaFileServertoaCacheManagertoinformthelatterwhenachangeismadetoanyofthedatadeliveredbytheFileServer.TwotypesofCallbacks:–acallbackwithawritablecopyoffile.–acallbackassociatedwiththeentireread-onlyvolumeTokensThetokenisasmallcollectionofdatathatcertifiesthattheuserhascorrectlyprovidedthepasswordassociatedwithaparticularAFSidentity.Whenausersuccessfullyauthenticates,theAFSauthenticationservicepassesatokentotheuser’sCacheManager.TheCacheManagerpresentsthetokentoAFSserverprocessesalongwithservicerequests,asproofthattheuserisgenuine.TheCacheManagerstorestokensintheuser’scredentialstructureinkernelmemory.AusercanhaveonlyonetokenpercellACL(AccessControlList)AFSACLsprovidemorerefinedaccesscontrolonadirectoryandallofthefilesinit.sevenaccesspermissions:–a(administer)–d(delete)–i(insert)–k(lock)–l(lookup)–r(read)–w(write)Threesystemgroups:–system:anyuser–system:authuser–system:administratorsAFSVsUFSAFSUFSProtectionatdirectorylevelProtectionatfilelevelOnlyuserwithrightACLpermissioncansetmodebitsNormalmodebitsset.Sevenaccesspermissions:a(administer)d(delete)i(insert)k(lock)l(lookup)r(read)w(write)Threeaccesspermissions:r(read),w(write),andx(execute).DifferentsetofaccesspermissionstoeachusersandgroupswithACLThreedefinedusersandgroupsAFSvs.NFS(I)NFSAFSInstalledBaseverylargesmall,growingsomewhatAccesTransparency(i.e.,nospecialcommandstogettofiles.Theylookliketheyarelocal)YesYesCachingMinimalFullAuthorizationGlobalGID/UIDKerberosSecurityStandardUnix(3rightstofilesand/ordirectories)ACL'sgrantingindividualorgroupsanycombinationofsevenrightstoentiredirectories•AFS,AndrewFileSystem;FermilabFinalEvaluationReportandImplementationRecommendations,FarhadAbar,GaryRoedigers,JosephStith2,MattWicks.May12,1992.AFSvs.NFS(II)NFSAFSLocationtransparency(i.e.willtheclientmachinecontinuetoworkifthefilesaremovedfromonelocationtoanother?)NoYesAccesstolocaldiskwhichisalsoservedtothenetworkBetterWorseLANandWANperformanceWorseBetterdedicatedServersSometimesUsuallyScalabilityofmanagementdemandsWorseBetterCommonnamespaceSometimesYesOnlinebackupNoYesOnlinevolumemoveNoYesAFSvs.NFS:ArchitectureArchitectureAFS3NFS3Fileserversandclientsformalogicaladministrativeunitcalledacell.Fileserversandclients.Eachfileserverismanagedindependently.Administrationbycollectionsoffilescalledvolumes.Administrationbyindividualfiles.AutomaticfilelocationtrackingbysystemprocessesandVolumeLocationDatabase.Mountpointsfortrackingfile'sphysicallocationsetbyadministratorsandusers.Statefulservers.Nearlystatelessservers.•TransarcCorporation,TheAFSFileSysteminDistributedComputingEnvironment,1996AFSvs.NFS:PerformancePerformanceAFS3NFS3Robustdiskcachingreducesfileserverandnetworkload.Memorycachingwithsmallbuffers.Servercallbacksguaranteecacheconsistency.Open-to-closesemantics.Attributescachedseveralhours.Time-basedcacheconsistencymaycauseinconsistenciestooccur.Attributescached3-30seconds.Replicasspreadtheloadamongpreferredservers.Noreplicationtoreduceload.Noreplicationtoreduceload.Excellentperformanceinwide-areaconfigurations.Inefficientinwide-areaconfigurations.Scaleable;maintainsperformanceinanysizeinstallation.Bestinsmall-tomedium-sizeinstallations.AFSvs.NFS:AvailabilityAvailabilityAFS3NFS3Read-onlyreplicationbyvolume.Automaticswitchovertoavailablereplica.Nostandarddatareplication.Filesremainavailabletousersduringreconfiguration.Filenamesremainthesame.Userslos