参考分析介绍ch10.pptx

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2025-04-10 发布于北京
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参考分析介绍ch10.pptx

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Chapter10:Mass-StorageSystems

Chapter10:Mass-StorageSystemsOverviewofMassStorageStructureDiskStructureDiskAttachmentDiskSchedulingDiskManagementSwap-SpaceManagementRAIDStructureStable-StorageImplementation

ObjectivesTodescribethephysicalstructureofsecondarystoragedevicesanditseffectsontheusesofthedevicesToexplaintheperformancecharacteristicsofmass-storagedevicesToevaluatediskschedulingalgorithmsTodiscussoperating-systemservicesprovidedformassstorage,includingRAID

OverviewofMassStorageStructureMagneticdisksprovidebulkofsecondarystorageofmoderncomputersDrivesrotateat60to250timespersecondTransferrateisrateatwhichdataflowbetweendriveandcomputerPositioningtime(random-accesstime)istimetomovediskarmtodesiredcylinder(seektime)andtimefordesiredsectortorotateunderthediskhead(rotationallatency)Headcrashresultsfromdiskheadmakingcontactwiththedisksurface--That’sbadDiskscanberemovableDriveattachedtocomputerviaI/ObusBussesvary,includingEIDE,ATA,SATA,USB,FibreChannel,SCSI,SAS,FirewireHostcontrollerincomputerusesbustotalktodiskcontrollerbuiltintodriveorstoragearray

Moving-headDiskMechanism

HardDisksPlattersrangefrom.85”to14”(historically)Commonly3.5”,2.5”,and1.8”Rangefrom30GBto3TBperdrivePerformanceTransferRate–theoretical–6Gb/secEffectiveTransferRate–real–1Gb/secSeektimefrom3msto12ms–9mscommonfordesktopdrivesAverageseektimemeasuredorcalculatedbasedon1/3oftracksLatencybasedonspindlespeed1/(RPM/60)=60/RPMAveragelatency=?latency(FromWikipedia)

HardDiskPerformanceAccessLatency=Averageaccesstime=averageseektime+averagelatencyForfastestdisk3ms+2ms=5msForslowdisk9ms+5.56ms=14.56msAverageI/Otime=averageaccesstime+(amounttotransfer/transferrate)+controlleroverheadForexampletotransfera4KBblockona7200RPMdis