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1、PrintArticlePage1of3IssueDate:OpenSystemseditionDecember2006BreakingtheBottleneckJaquiLynchjaqui.lynch@mainline.comAnoverviewofGPFScomponentsandterminologyAsmorehighI/Oworkloadsmoveontomidrangesystems,thecapabilitytoreliablyprovidehighI/Obandwidthisbe
2、comingmorecritical.High-performancecomputing(HPC)hashadthisrequirementforsometimeanditwasaddressedonthescalableparallelsystemsin1998withtheinitialreleasesoftheGeneralParallelFile-System(GPFS).GPFShasnowmovedoutoftheHPCarenaandcanbeusedforcommercialmul
3、tinodeworkloadstoprovidedataaccess.GPFSisahigh-performance,shared-diskfile-systemthatsupportsdataaccessfrommultiplenodestomultipleterabytesofdiskinasinglefile-systemwithsupportforfileslargerthan2GB.Itallowsapplicationstosimultaneouslyaccessdatafromany
4、nodethathasGPFSmounted,whilestillprovidingperformance,reliabilityandconsistency.DataAccessNormalUNIX*filesystemsprovideaccesstofilesbutlockatthefilelevel.Thismeansthatoneormoreapplicationscouldbereadingfromthefile,butonlyonecanbewriting.Onhigh-writewo
5、rkloads,thisseriouslyaffectsperformanceandthroughput.GPFSaddressesthisbyusingbyte-rangelockingtoallowmultipletaskstoreadfrom,and/orwriteto,afilewithoutserialization,whilestillmaintainingconsistency.ThedataitselfisstoredintheGPFS,whichisastripingfilesy
6、stemthatdistributesdiskblocksacrossallthedisks.Thestripingisimplementedinthefilesystem,notthelogicalvolumemanager(LVM).Largefilesaredividedintoequalsizedblocksandtheconsecutiveblocksareplacedondifferentdisksinaround-robinfashion.Tofurtherimprovethroug
7、hput,GPFSmakesextensiveuseofread-aheadandwrite-aheadcaching.Toprovidedataconsistency,atoken-managementsystemisusedtotrackwhichnodesownwhichlocks.DataisprefetchedintotheGPFSbufferpool,whereit'smadeavailabletotheapplications.GPFSalsoprovidesanadditional
8、modeofaccesstothenormalmodes(read,writeandexecute).Thisnewmode,called"c"or"control,"specifieswhomanagestheaccesscontrollist(ACL)forafileapartfromthedefaultsofownerandroot.ComponentsandTerminologyThefollowingisalistofusefulGPFScomponentsandterm
