An Implementation of a Log Structured File System for UNIX

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1、AnImplementationofaLog-StructuredFileSystemforUNIXMargoSeltzer±HarvardUniversityKeithBostic±UniversityofCalifornia,BerkeleyMarshallKirkMcKusick±UniversityofCalifornia,BerkeleyCarlStaelin±Hewlett-PackardLaboratoriesABSTRACTResearchresults[ROSE91]demonstratethatalog-structured®lesystem(LF

2、S)offersthepotentialfordramaticallyimprovedwriteperformance,fasterrecoverytime,andfaster®lecreationanddeletionthantraditionalUNIX®lesystems.ThispaperpresentsaredesignandimplementationoftheSprite[ROSE91]log-structured®lesystemthatismorerobustandintegratedintothevnodeinterface[KLEI86].Mea

3、surementsshowitsperformancetobesuperiortothe4BSDFastFileSystem(FFS)inavarietyofbenchmarksandnotsigni®cantlylessthanFFSinanytest.Unfortunately,anenhancedversionofFFS(withreadandwriteclustering)[MCVO91]providescomparableandsometimessuperiorperformancetoourLFS.However,LFScanbeextendedtopro

4、videadditionalfunctionalitysuchasembeddedtransactionsandversioning,noteasilyimplementedintraditional®lesystems.1.IntroductionThelog-structured®lesystem,asproposedin[OUST88],attemptstoaddressbothoftheseprob-EarlyUNIX®lesystemsusedasmall,®xedlems.ThefundamentalideaofLFSistoimproveblocksiz

5、eandmadenoattempttooptimizeblock®lesystemperformancebystoringall®lesystemplacement[THOM78].Theyassigneddiskdatainasingle,continuouslog.Sucha®lesystemaddressestonewblocksastheywerecreated(preal-isoptimizedforwriting,becausenoseekisrequiredlocation)andwrotemodi®edblocksbacktotheirbetweenw

6、rites.Itisalsooptimizedforreading®lesoriginaldiskaddresses(overwrite).Inthese®lesys-writtenintheirentiretyoverabriefperiodoftimetems,thediskbecamefragmentedovertimesothat(asisthenorminUNIXsystems),becausethe®lesnew®lestendedtobeallocatedrandomlyacrosstheareplacedcontiguouslyondisk.Final

7、ly,itprovidesdisk,requiringadiskseekper®lesystemreadortemporallocality,inthatitisoptimizedforaccess-writeevenwhenthe®lewasbeingreadsequentially.ing®lesthatwerecreatedormodi®edatapproxi-TheFastFileSystem(FFS)[MCKU84]matelythesametime.dramaticallyincreased®lesystemperformance.ItT