38-An Introduction to Disk Drive Modeling.pdf38-An Introduction to Disk Drive Modeling.pdf

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ANINTRODUCTIONTODISKDRIVEMODELINGCHRISRUEMMLERANDJOHNWILKESHEWLETTPACKARDLABORATORIES,PALOALTO,CAMUCHRESEARCHINI/OSYSTEMSISBASEDONDISKDRIVESIMULATIONMODELS,BUTHOWGOODARETHEYANACCURATESIMULATIONMODELSHOULDEMPHASIZETHEPERFORMANCECRITICALAREASTHISPAPERHASBEENPUBLISHEDINIEEECOMPUTER27317–29,MARCH1994ITSUPERSEDESHPLABSTECHNICALREPORTSHPL–93–68REV1ANDHPL–OSR–93–29COPYRIGHT1994IEEEINTERNALORPERSONALUSEOFTHISMATERIALISPERMITTEDHOWEVER,PERMISSIONTOREPRINT/REPUBLISHTHISMATERIALFORADVERTISINGORPROMOTIONALPURPOSESORFORCREATINGNEWCOLLECTIVEWORKSFORRESALEORREDISTRIBUTIONMUSTBEOBTAINEDFROMTHEIEEETORECEIVEMOREINFORMATIONONOBTAININGPERMISSION,SENDABLANKEMAILMESSAGETOINFOPUBPERMISSIONIEEEORGNOTETHISFILEWASOBTAINEDBYSCANNINGANDPERFORMINGOCRONTHEIEEEPUBLISHEDCOPYASARESULT,ITMAYCONTAINTYPOGRAPHICOROTHERERRORSTHATARENOTINTHEPUBLISHEDVERSIONMINORCLARIFICATIONSANDUPDATESHAVEBEENMADETOTHEBIBLIOGRAPHY1MODERNMICROPROCESSORTECHNOLOGYISADVANCINGATANINCREDIBLERATE,ANDSPEEDUPSOF40TO60PERCENTCOMPOUNDEDANNUALLYHAVEBECOMETHENORMALTHOUGHDISKSTORAGEDENSITIESAREALSOIMPROVINGIMPRESSIVELY60TO80PERCENTCOMPOUNDEDANNUALLY,PERFORMANCEIMPROVEMENTSHAVEBEENOCCURRINGATONLYABOUT7TO10PERCENTCOMPOUNDEDANNUALLYOVERTHELASTDECADEASARESULT,DISKSYSTEMPERFORMANCEISFASTBECOMINGADOMINANTFACTORINOVERALLSYSTEMBEHAVIORNATURALLY,RESEARCHERSWANTTOIMPROVEOVERALLI/OPERFORMANCE,OFWHICHALARGECOMPONENTISTHEPERFORMANCEOFTHEDISKDRIVEITSELFTHISRESEARCHOFTENINVOLVESUSINGANALYTICALORSIMULATIONMODELSTOCOMPAREALTERNATIVEAPPROACHES,ANDTHEQUALITYOFTHESEMODELSDETERMINESTHEQUALITYOFTHECONCLUSIONS;INDEED,THEWRONGMODELINGASSUMPTIONSCANLEADTOERRONEOUSCONCLUSIONSNEVERTHELESS,LITTLEWORKHASBEENDONETODEVELOPORDESCRIBEACCURATEDISKDRIVEMODELSTHISMAYEXPLAINTHECOMMONPLACEUSEOFSIMPLE,RELATIVELYINACCURATEMODELSWEBELIEVETHEREISMUCHROOMFORIMPROVEMENTTHISARTICLEDEMONSTRATESANDDESCRIBESACALIBRATED,HIGHQUALITYDISKDRIVEMODELINWHICHTHEOVERALLERRORFACTORIS14TIMESSMALLERTHANTHATOFASIMPLEFIRSTORDERMODELWEDESCRIBETHEVARIOUSDISKDRIVEPERFORMANCECOMPONENTSSEPARATELY,THENSHOWHOWTHEIRINCLUSIONIMPROVESTHESIMULATIONMODELTHISENABLESANINFORMEDTRADEOFFBETWEENEFFORTANDACCURACYINADDITION,WEPROVIDEDETAILEDCHARACTERISTICSFORTWODISKDRIVES,ASWELLASABRIEFDESCRIPTIONOFASIMULATIONENVIRONMENTTHATUSESTHEDISKDRIVEMODELCHARACTERISTICSOFMODERNDISKDRIVESTOMODELDISKDRIVES,WEMUSTUNDERSTANDHOWTHEYBEHAVETHUS,WEBEGINWITHANOVERVIEWOFTHECURRENTSTATEOFTHEARTINNONREMOVABLEMAGNETICDISKDRIVESWITHEMBEDDEDSCSISMALLCOMPUTERSYSTEMSINTERCONNECTCONTROLLERS,SINCETHESEAREWIDELYAVAILABLEDISKDRIVESCONTAINAMECHANISMANDACONTROLLERTHEMECHANISMISMADEUPOFTHERECORDINGCOMPONENTSTHEROTATINGDISKSANDTHEHEADSTHATACCESSTHEMANDTHEPOSITIONINGCOMPONENTSANARMASSEMBLYTHATMOVESTHEHEADSINTOTHECORRECTPOSITIONTOGETHERWITHATRACKFOLLOWINGSYSTEMTHATKEEPSITINPLACETHEDISKCONTROLLERCONTAINSAMICROPROCESSOR,SOMEBUFFERMEMORY,ANDANINTERFACETOTHESCSIBUSTHECONTROLLERMANAGESTHESTORAGEANDRETRIEVALOFDATATOANDFROMTHEMECHANISMANDPERFORMSMAPPINGSBETWEENINCOMINGLOGICALADDRESSESANDTHEPHYSICALDISKSECTORSTHATSTORETHEINFORMATIONBELOW,WELOOKMORECLOSELYATEACHOFTHESEELEMENTS,EMPHASIZINGFEATURESTHATNEEDTOBECONSIDEREDWHENCREATINGADISKDRIVEMODELITWILLBECOMECLEARTHATNOTALLTHESEFEATURESAREEQUALLYIMPORTANTTOAMODEL’SACCURACYTHERECORDINGCOMPONENTSMODERNDISKSRANGEINSIZEFROM13TO8INCHESINDIAMETER;25,35,AND525INCHESARETHEMOSTCOMMONSIZESTODAYSMALLERDISKSHAVELESSSURFACEAREAANDTHUSSTORELESSDATATHANTHEIRLARGERCOUNTERPARTS;HOWEVER,THEYCONSUMELESSPOWER,CANSPINFASTER,ANDHAVESMALLERSEEKDISTANCESHISTORICALLY,ASSTORAGEDENSITIESHAVEINCREASEDTOWHERE2–3GIGABYTESCANFITONASINGLEDISK,THENEXTSMALLERDIAMETERINTHESERIESHASBECOMETHEMOSTCOSTEFFECTIVEANDHENCETHEPREFERREDSTORAGEDEVICE2INCREASEDSTORAGEDENSITYRESULTSFROMTWOIMPROVEMENTSTHEFIRSTISBETTERLINEARRECORDINGDENSITY,WHICHISDETERMINEDBYTHEMAXIMUMRATEOFFLUXCHANGESTHATCANBERECORDEDANDREADBACK;CURRENTVALUESAREAROUND50,000BITSPERINCHANDWILLAPPROXIMATELYDOUBLEBYTHEENDOFTHEDECADETHESECONDCOMESFROMPACKINGTHESEPARATETRACKSOFDATAMORECLOSELYTOGETHER,WHICHISHOWMOSTOFTHEIMPROVEMENTSAREOCCURRINGCURRENTVALUESAREABOUT2,500TRACKSPERINCH,RISINGTOPERHAPS20,000TPIBYTHEENDOFTHEDECADETHEPRODUCTOFTHESETWOFACTORSWILLPROBABLYSUSTAINAGROWTHRATEABOVE60PERCENTPERYEARTOTHEENDOFTHEDECADEASINGLEDISKCONTAINSONE,TWO,ORASMANYASADOZENPLATTERS,ASSHOWNINFIGURE1THESTACKOFPLATTERSROTATESINLOCKSTEPONACENTRALSPINDLEALTHOUGH3,600RPMWASADEFACTOSTANDARDFORMANYYEARS,SPINDLEROTATIONSPEEDHASINCREASEDRECENTLYTOASMUCHAS7,200RPMTHEMEDIANROTATIONSPEEDISINCREASINGATACOMPOUNDRATEOFABOUT12PERCENTPERYEARAHIGHERSPINSPEEDINCREASESTRANSFERRATESANDSHORTENSROTATIONLATENCIESTHETIMEFORDATATOROTATEUNDERTHEHEAD,BUTPOWERCONSUMPTIONINCREASESANDBETTERBEARINGSAREREQUIREDFORTHESPINDLETHESPINSPEEDISTYPICALLYQUOTEDASACCURATEWITHIN05TO1PERCENT;INPRACTICE,THEDISKSPEEDSVARYSLOWLYAROUNDTHENOMINALRATEALTHOUGHTHISISPERFECTLYREASONABLEFORTHEDISK’SOPERATION,ITMAKESITNEARLYIMPOSSIBLETOMODELTHEDISK’SROTATIONALPOSITIONSOME100200REVOLUTIONSAFTERTHELASTKNOWNOPERATIONFORTUNATELY,MANYI/OOPERATIONSOCCURINBURSTS,SOTHEUNCERTAINTYAPPLIESONLYTOTHEFIRSTREQUESTINTHEBURS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编号:201401051948266814    类型:共享资源    大小:290.00KB    格式:PDF    上传时间:2014-01-05
  
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