中科大操作系统原理与实现课件12_MassStorageSystems1.pdf
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中科大操作系统原理与实现课件12_MassStorageSystems1.pdf

中科大操作系统原理与实现课件12_MassStorageSystems1.pdf

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操作系统原理与设计第12章Mass-Storagestructure(外存)陈香兰中国科学技术大学计算机学院2009年09月01日......提纲OverviewofMassStorageStructureDiskStructureDiskSchedulingDiskManagementSwap-SpaceManagement小结和作业......OverviewofMassStorageStructureIIMagneticdisksprovidebulkofsecondarystorageofmoderncomputersIDrivesrotateat60to200timespersecondITransferrateisrateatwhichdataflowbetweendriveandcomputerIPositioningtime(random-accesstime)istimetomovediskarmtodesiredcylinder(seektime)andtimefordesiredsectortorotateunderthediskhead(rotationallatency)IHeadcrashresultsfromdiskheadmakingcontactwiththedisksurfaceIThat’sbadIDiskscanberemovable......OverviewofMassStorageStructureIIIDriveattachedtocomputerviaI/ObusIBussesvary,includingEIDE,ATA,SATA,USB,FibreChannel,SCSIIHostcontrollerincomputerusesbustotalktodiskcontrollerbuiltintodriveorstoragearray......OverviewofMassStorageStructure(Cont.)IMagnetictapeIWasearlysecondary-storagemediumIRelativelypermanentandholdslargequantitiesofdataIAccesstimeslowIRandomaccess∼1000timesslowerthandiskIMainlyusedforbackup,storageofinfrequently-useddata,transfermediumbetweensystemsIKeptinspoolandwoundorrewoundpastread-writeheadIOncedataunderhead,transferratescomparabletodiskI20-200GBtypicalstorageICommontechnologiesare4mm,8mm,19mm,LTO-2andSDLTOper......DiskStructureIIDiskdrivesareaddressedaslarge1-Darraysoflogicalblocks,Ithelogicalblockisthesmallestunitoftransfer.Iusually,512BIThe1-Darrayoflogicalblocksismappedintothesectorsofthedisksequentially.ICylinder:track:sectorISector0isthefirstsectorofthefirsttrackontheoutermostcylinder.IMappingproceedsinorderthroughthattrack,thentherestofthetracksinthatcylinder,andthenthroughtherestofthecylindersfromoutermosttoinnermost.......DiskStructureII......DiskStructureIIIIHowever,inpractise,themappingisdifficult,because1.Defectivesectors2.Sectors/track=6constant)zonesofcylinder......DiskSchedulingIITheOSisresponsibleforusinghardwareefficiently—for