disk architecture

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1、Module8DiskArchitectureDiskArchitecture11-20038-1©2001,2003InternationalBusinessMachinesCorporationObjectivesAttheendofthismodule,youwillbeableto:®DescribetheDynamicServerchunkandpagestructure®Explainhowpagesareallocatedwithinextents®Explainthedifferencebetweentableandindexextents®Descri

2、betherelationshipbetweenchunksandDBSPACES®Describetheoverheadpagesinvarioustypesofchunks®Describethestructureofadbspace,blobspace,andsbspace®Usetheoncheckcommandtodisplayreportsaboutspaceallocation,tblspaceusage,andindexusage®Useonstattodisplaydbspaceandchunkinformation8-28-2DiskArchitec

3、tureUnitofPhysicalDiskSpace:Chunk/dev/rxy0h/dev/chunk110000KB10000KBUnix(cooked)fileRawDevicePieceofRawDevicepath=/dev/cook-001path=/dev/raw-001path=/dev/raw-001offset=0KBoffset=0KBoffset=5000KBsize=10000KBsize=10000KBsize=10000KB/dev/rxy0f5000KB20000KB10000KB8-3Achunkisaunitofdiskorphys

4、icalspacethatisassignedtotheserver.Achunkcanbearawdevice(character-specialdevice),apieceofarawdevice,oraUNIXfile(cookedfile).Whenyouassignachunktotheserver,youdefinethechunkusingthefollowingthreevalues:PathnameThepathnameofthefileortherawdevicenametobeusedforthechunk.OffsetThephysicaldis

5、tance,specifiedinkilobytes,fromthebeginningofthedevicetowherereadingandwritingforthedevicebegins.Ifcreatingchunksthatusecookedfiles,useanoffsetof0.Anon-0offsetisonlytobeusedforrawdevices.SizeTheamountofspace,specifiedinkilobytes,allocatedtobeusedinarawdevicestartingfromtheoffset,orthesiz

6、eoftheUNIXfileusedforthechunk.ChunkLimitAserverhasalogicallimitof32,767chunks(thelimitis2047chunksinpre-9.4versionsofIDS).However,theUNIXkernelmighthavealimittothenumberoffilesaprocesscanhaveopenthatsupersedestheserverlimit.DiskArchitecture8-3EnablingLargeChunkSupport(9.4)Enablelargechun

7、ksupportbyexecutingthefollowingcommand:onmode-BCnwherenisoneofthefollowingconversionstagelevels:®Stage1•Largechunksandlargeoffsetsenabled•Writestosmallchunkscontinuetouseoldpageformat•Reversionisstillpossible®Stage2•Allpagesareconvertedto9.4formatastheyaremodifiedduringno