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8/6/2019 Tradeoffs RAID5 RAID10
1/21
Comprehending the Tradeoffs
between Deploying Oracle
Database on RAID 5 and RAID 10
Storage Configurations
ADellTechnicalWhitePaper
Database Solutions Engineering
By Sudhansu Sekhar and Raghunatha M
Dell Product Group
April 2009
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UsingRAID10ComparedtoRAID5ConfigurationsforOracleDatabaseDeploymentsTradeoffs
Pageii
ExecutiveSummaryRedundantArrayofIndependentDisks(RAID)technologyisusedtoimproveperformanceand
availabilityoftheunderlyingstoragearraysforanyapplication.WithRAIDimplementations,
performanceisimprovedbydistributingI/Oacrossmanyphysicaldisksandavailabilityisincreasedwith
thedatarebuildingcapability.Butbothhighavailabilityandhighperformancecomesataprice,which
aredifferentfordifferentRAIDimplementations.
Mostofthetimedatabaseandstorageadministratorsasktheageoldquestionwhethertogowith
RAID10orRAID5fortheirdatabasedeployment.Customersstruggletomakerighttradeoffsbetween
thesetwoRAIDimplementationsfortheirdatabasedeployments. Thiswhitepaperevaluatesdifferent
tradeoffsincludingperformance,cost,andavailabilitywhileevaluatingRAID10comparedtoRAID5.
ThiswillhelpthecustomerstomakeinformeddecisionstochoosetherightRAIDimplementationfor
theirspecificworkloadwhichcanmeettheirdesiredperformanceandavailabilityrequirements.
THISWHITEPAPERISFORINFORMATIONALPURPOSESONLY,ANDMAYCONTAINTYPOGRAPHICAL
ERRORSANDTECHNICALINACCURACIES.THECONTENTISPROVIDEDASIS,WITHOUTEXPRESSOR
IMPLIEDWARRANTIESOFANYKIND.
2009DellInc.Allrightsreserved.Reproductionofthismaterialinanymannerwhatsoeverwithout
theexpresswrittenpermissionofDellInc.isstrictlyforbidden.Formoreinformation,contactDell.
Dell,theDELLlogo,andtheDELLbadgearetrademarksofDellInc.EMCisaregisteredtrademarkofEMCintheUnitedStatesand/orothercountries.OracleandRACareregisteredtrademarksofOracleintheUnitedStatesand/orothercountries.
Othertrademarksandtradenamesmaybeusedinthisdocumenttorefertoeithertheentitiesclaiming
themarksandnamesortheirproducts.Delldisclaimsproprietaryinterestinthemarksandnamesof
others.
8/6/2019 Tradeoffs RAID5 RAID10
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ContentsExecutiveSummary................................................................................................................................... ii
Introduction.............................................................................................................................................. 4
OverviewofRAID...................................................................................................................................... 4
RAIDImplementationinDell/EMCStorageArrays............................................................................ 5
RAIDTradeoffs.......................................................................................................................................... 5
PerformanceTradeoffRAID10ComparedtoRAID5.......................................................................... 6
TestConfiguration................................................................................................................................. 6
Test
Cases
..............................................................................................................................................
6
OLTPWorkload..................................................................................................................................... 6
ResultsandAnalysis.............................................................................................................................. 7
OLAPWorkload..................................................................................................................................... 9
ResultsandAnalysis.............................................................................................................................. 9
CostTradeoffRAID10ComparedtoRAID5...................................................................................... 11
TestConfigurations............................................................................................................................. 11
TestCases............................................................................................................................................ 12
ResultsandAnalysis............................................................................................................................ 12
AvailabilityTradeoffRAID10comparedtoRAID5.............................................................................. 14
TestConfigurations............................................................................................................................. 14
TestCases............................................................................................................................................ 14
ResultsandAnalysis............................................................................................................................ 14
FourQuadrantAnalysis........................................................................................................................... 15
Conclusion............................................................................................................................................... 18
GLOSSARY
................................................................................................................................................
19
References.............................................................................................................................................. 21
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IntroductionConfigurationoftheunderlyingstoragesubsystemisoneofthemostcriticaltaskswhiledeploying
applications.ForI/OintensiveapplicationslikeOracleDatabases,thestorageconfigurationcanbe
extremelycomplex.Storageanddatabaseadministratorsneedtocomprehendseveralperformance
criteriawhileconsideringthestoragedesign.Someoftheimportantstorageoptionsthatneedcareful
attentionareRAIDconfigurations,cacheconfigurations,disktypes,andsoon.Ofthese,onetopicof
debateistheRAIDconfigurationforstoragearrays.
Fromaperformanceperspective,RAID10isclaimedtobetheidealRAIDchoicefordatabase
deployments.However,customerssometimeshavetomakecosttradeoffs,whichforcethemaway
fromRAID10andleadthemtochoosethemorecosteffectiveRAID5configuration.
BothRAID10andRAID5configurationshaveadvantagesanddisadvantagesandaresuitableforspecific
I/Opatterns. ThiswhitepaperprovidesrecommendationsonusingRAID10andRAID5fordifferent
databaseworkloads.Thispaperalsoexaminesseveraltradeoffs(forexample,performancetradeoff,
costtradeoff,andavailabilitytradeoff)whiledeployingOracleDatabaseswithRAID10comparedto
RAID5.AfourquadrantanalysiswasprovidedtohelpcustomerstochoosetheRAIDconfigurationsfor
databaseswithmixedusedeployment,wherecustomersrunonlinetransactionprocessing(OLTP)
duringthedayandDSSworkloadatnight.Thiswillhelpthedatabaseandstorageadministratorsto
makeaninformeddecisionwhenplanningtheircomplexdatabasedeployments.
OracleDatabasehasseveralcomponentsandeachofthesecomponentscanhavedifferentI/Opatterns.
Componentslikeonlineredologs,controlfiles,tempandundotablespacesarewriteintensive.Onthe
otherhand,datafilesforOracleDatabasecanberead orwriteintensive,dependingonthetypeof
application
which
is
accessing
the
database.
As
a
result,
different
RAID
technologies
can
be
appropriate
fordifferentdatabasecomponents.Customerscanevenmixandmatchconfigurationsfortheir
databasedeploymentbyplacingdifferentcomponentsofOracleDatabaseindifferentRAIDgroups.
Thesetypesofconfigurationsareanalyzed,andrecommendationsareprovidedinthiswhitepaper.
OverviewofRAIDTheobjectiveoftheRAIDtechnologyistoaccomplishthefollowinggoals:
1. Improvethediskread/writeperformance(byparallelizingtheI/Oovermultipledisks)
2. Improveredundancy(byintroducingdatarecoverycapabilityintheeventofdiskfailure)
SeveralRAIDtechnologiesareavailabletoachievebetterdiskperformanceanddataredundancy.Below
arethemostcommonlyusedRAIDconfigurationsusedfortheimplementationofOracleDatabase:
RAID10(alsoknownasstripeandmirror)ThistechniqueisamixofRAID1(whichis
mirroring)andRAID0(whichisstriping).WithRAID10,dataisspreadacrossmultipledisks(to
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improveperformance),andthestripeddataismirroredasadifferentdataset(toprovide
redundancy).
RAID5Theimplementationofamathematicalexclusiveor(XOR)isamethodthatusesparity
toreconstructdatafromafaileddrive.RAID5doesnotmirrorthewholesetofdatatobuild
redundancyintothesetup.Dataisstripedacrossallthediskstoalsoimprovetheperformance
inRAID5.
RAIDImplementationinDell/EMCStorageArraysDifferentstoragevendorsimplementedtheRAIDtechnologiesinseveralways.Belowisthedescription
onthewayRAID10andRAID5areimplementedinDell/EMCstoragearrays.
ForDell/EMCstoragearrays,RAID10takescareofbothdatastripingandmirroring.First,thedatais
stripedacrossallthedisksintheRAIDgroup.ThisensurestheoptimumperformancefortheRAID
configuration. Oncethedataisstripedacrossallthedisks,thedatasetsgetmirroredinsidethe
available
disks
to
create
the
redundant
copies.
Foroptimalredundancy,EMCrecommendstoconfiguretheRAID5witha3+1configuration.Witha3+1
configuration,onediskisusedforstoringparitydataforeverythreedisksthatareusedintheRAID
configuration.Forstoragesystems,RAID5canbeimplementedwith3 to16diskRAIDgroups.But
considerationsshouldbetakenwhileselectingthenumberofdisksfortheRAIDgroup.Thelargerthe
sizeoftheRAIDgroup,themoretimeittakestorebuildthedataintheeventofadiskfailure.
RAIDTradeoffsAsdiscussedintheprevioussection,RAIDimplementationsimproveperformanceandredundancy.
However,performanceimprovementandredundancycomewithcostasalargeramountofdisksis
required,forexample:
Forthesamesizeofdatabase,RAID10requiresmoredisksthanRAID5toachievethedesired
dataavailability.
RAID5requiresmoretimetoreconstructthefaileddataincaseofdiskfailure.
RAID5hastodealwithparityoverheadfordiskwrites.
CustomersneedtoconsiderthefollowingtradeoffsbeforeimplementingaparticularRAIDtechnology:
Performancetradeoff theperformancebenefitofpreferringRAID10toRAID5withthe
desiredI/Opattern
CosttradeoffthecostbenefitofeitherRAID10orRAID5implementation
Availabilitytradeofftheamountoftimerequiredtorecoverdatafromafaileddiskscenario
ThefollowingsectionsdiscusstheaboveconsiderationsinthecontextofOracleDatabasedeployedon
RAID10comparetoRAID5configurations.
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PerformanceTradeoffRAID10ComparedtoRAID5ThissectionprovidestheperformanceanalysisforbothRAID10andRAID5configurationsfordifferent
databaseworkloadsandI/Opatterns.Theanalysiscanbeusedfordeterminingtheperformance
tradeoffsbetweenRAID10andRAID5implementationsfordifferentdatabaseworkloads.
TestConfigurationFortheperformancetradeofftest,twoOracle11GR1(11.1.0.7)twonodeRACclustersweredeployed.
OneRACclusterwasdeployedwithRAID10layoutandtheotherclusterwithRAID5layout.Bothofthe
RAID10andRAID5wascreatedfromeightdisks.Thefollowinghardwareandsoftwarecomponents
wereusedforthesetwoclusters:
Hardware
Components
RAID
10
and
RAID
5
Server 2xR710
Storage CX4480
FCswitch BrocadeSW5000
Networkswitch DellPowerConnect5448
Software
Operatingsystem RHEL5.2
OracleRDBMS(withRAC) EE11GR1(11.1.0.7)
EMCPowerPath V5.1.0
Database
Databasesize 400GB
BenchmarkTools
QuestBenchmark
Factory(OLTPworkloads)
V5.5.1
ORION(OLAPworkload) 10.2
TestCasesThetestcasesweredividedintotwomajorcategories,OLTPworkloadsandOnLineAnalytical
Processing(OLAP)workloads:
OLTPWorkloadQuestBenchmarkFactoryhasaframeworkwhichprovidesindustrystandardTPCCperformanceruns.
QuestBenchmarkFactoryTPCCworkloadisdesignedforonlinetransactionprocessingenvironment
withmorereads(70%)andlesswrites(30%).AspartofTPCCperformancerun,thedatabasewas
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loadedwith400GBofdata.Transactionswerecarriedoutwithincreasinguserloads.Theperformance
statisticswerecollectedforeachoftheuserloads.
ResultsandAnalysisForanOLTPworkload,performanceistypicallymeasuredintermsoftransactionspersecond(TPS)and
theresponsetime.Fromaperformanceprospective,thedatabaseshouldbeabletomeettheTPS
requirementwithinpermissibleresponsetime.
QuestBenchmarkFactoryTPCCgeneratedthetransactionsforthedatabase.Thetransactionsper
secondandtheresponsetimemetricsarecapturedforboththeRAID10andtheRAID5configurations.
Figure1providestheTPSwithvaryinguserloads,andFigure2providestheresponsetimeanalysisfor
varyinguserloadsforboththeRAID10andtheRAID5configurations.
Figure1:TransactionsperSecond(TPS)AnalysisRAID10ComparedtoRAID5
0
10
20
30
40
50
60
70
TPS
Userload
TransactionPerSeconds(TPS)Vs.UserLoad
TPSRAID10
TPSRAID5
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Figure2:ResponseTimeAnalysisRAID10ComparedtoRAID5
FromFigure1,wecanobservethatboththeRAIDconfigurationscouldprovidethesameTPSaroundthe
900userloadmarks.Butbeyondtheloadgeneratedby900usersinthisspecificbenchmark,theRAID5
clusterisnotabletokeeppacewithRAID10cluster.
TheresponsetimeanalysisprovidesasimilartrendfortheRAID10andtheRAID5clusters.Response
timeisthetimeelapsedfortheSQLroundtrip,inotherwords,thetimeelapsedfromthetimethe
BenchmarkFactoryclientsubmitstheSQL,tothetimeatwhichtheclientgetstheresponse.Fromthe
responsetimeplot(Figure2),wecanobservethattheresponsetimeincreasessignificantlyafterthe
900userloadmarkforRAID5cluster.Aswecansee,theresponsetimeexceeds2msbeyond900user
loadsfortheRAID5configuration,whiletheRAID10configurationprovidesresponsetimebelow2ms
upto1100userloads.
Asaresult,forOLTPworkloads(loadswithroughlya70/30readtowriteratio),theRAID5performance
canmatchtheRAID10configurationuptoacertainuserload.BeyondthatRAID10performanceis
betterthanthatofRAID5configuration.Inotherwords,RAID10willprovidebetterTPSwithless
responsetimecomparedtoRAID5configurationbeyondcertainuserload.Thisbehaviorisexpected
becauseoftheparitywritepenaltyassociated(forwriteactivities)withRAID5.
Forlightlyloadeddatabaseswithverylowreadandwriteworkloads,theperformancedegradationmay
notbenoticedfortheRAID5configuration.Inotherwords,bothRAID10andRAID5maybeusedto
deploylightlyloadeddatabases.Inthisscenario,theparitywritepenaltywillbelessbecauseofthelight
workload.
0
2
4
6
8
10
12
Response
time(ms)
Userload
ResponseTimeVs.UserLoad
AvgResponseTime
RAID10
AvgResponseTime
RAID5
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OLAPWorkloadORIONwasusedtosimulatetheonlineanalyticalprocessing(OLAP)workload.OLAPworkloadsoften
comprisefulltablescans,longrunningreports,andbackupjobs.Additionally,theI/OsizeofOLAPis
muchlargercomparedtoOLTP,mostlyintherangeof1MB.Consequently,thecharacteristicofthe
overalldatathroughput(measuredinMegabytespersecond)isofinterestforthesetypesofworkloads.
Databaseswerestressedwithbothlargesequentialreadandlargesequentialwriteoperations.Also,the
readandwriteratiowasvariedtoanalyzethethroughputbehaviorwithvaryingqueuelength.
ResultsandAnalysisWithORION,theI/Othroughputswerecapturedforlargesequentialwritesandlargesequential
readswith1MBofI/Osize.ThethroughputwascomparedforboththeRAID10andRAID5
configurations.
Figure3:ThroughputAnalysisforLargeSequentialWritesRAID10ComparedtoRaid5
Figure3providesacomparativeanalysisofthethroughputforlargesequentialwritesforRAID10and
RAID5configurations.TheXaxisrepresentsthenumberofoutstandingI/OsandtheYaxisrepresents
thethroughputinMBps.Aswecanobserve,theRAID10throughputoutperformstheRAID5
configurationforlargesequentialwrites.Thisbehaviorisexpectedbecauseoftheparitywritepenalty
associatedwiththeRAID5configuration.
0
20
40
60
80
100
120
140
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
MBps
NumberofOutstandingIOs
ThroughputVs.OutstandingIOs
LargeSequentialWrites
Raid5_Writes
Raid10_Writes
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Figure4:ThroughputAnalysisforLargeSequentialReadsRAID10ComparedtoRaid5
Figure4providesacomparativeanalysisofthethroughputforlargesequentialreadsforRAID10and
RAID5configurations.TheXaxisrepresentsthenumberofoutstandingI/OsandYaxisrepresentsthe
throughputinMBps.Aswecanobserve,theRAID5configurationcanmatchtheRAID10configuration
forlargesequentialreads.Theobservedpatternisexpected,giventhatthereisnoparitywritepenalty
associatedwiththeRAID5configurationforreadoperations.
Asmentionedearlier,thereadandwriteratiowasvariedtoanalyzethethroughputvariationswith
differentworkloads. Foranyparticularreadandwriteratio(e.g.10%Read+90%Write),the
throughputwascapturedbothforRAID10andRAID5configurations.Itwasobservedthatforallread
andwritemix,RAID10configurationgivesabetterthroughputcomparedtoRAID5configuration. The
percentageofthroughputincreasewascalculatedforeachofthesereadandwritemixesandplottedas
showninFigure5. TheXaxishasthedatapointforthedifferentreadandwritemixes(forexample,
0R+100Windicates0%readand100%write,10R+90Windicates10%readand90%Write,andsoon)
andtheYaxishasthedatapointforthepercentageofthroughputincreasefortheRAID10
configurationcomparedtotheRAID5configuration.
0
50
100
150
200
250
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
MBps
NumberofOutstandingIOs
ThroughputVs.OutstandingIOs
LargeSequentialReads
Raid5
Raid10
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Figure5:ThroughputanalysisforReadandwriteWorkloadMix
AswecanseefromFigure5,thepercentageofthroughputgainofRAID10overRAID5increaseswitha
higherpercentageofwriteoperations.ThethroughputgainforRAID10configurationsvariesfroma
minimumof12%(for0%write)toamaximumof45%(for100%write).Itisnecessarytonotethatthese
maximumandminimumvaluescanvarydependingupontheread/writecacheconfigurationforthe
storagearrays.However,theoverallrecommendation(fromtheanalysisofFigure5)isthatcustomers
maychoosetodeployRAID5(withminimalperformanceimpact),iftheirapplicationismostlyread
intensive.Incontrast,foreverywriteintensiveapplication,RAID10isrecommendedforbetter
performance.
CostTradeoff
RAID
10
Compared
to
RAID
5
ThissectionprovidesthecostbenefitanalysisforbothRAID10andRAID5implementations.Because
RAID5implementationsprovidemoreusablespacecomparedtoRAID10implementations,thissection
assistsintheanalysisofstoragespaceandtounderstandthecostbenefitswhileimplementingRAID5.
TestConfigurationsFollowingarethedetailsofthestoragearrayandthedisksusedforthecosttradeoffanalysis.
Hardware Components Details
Storage CX4480
Harddisk 300GB(RAWspace)
265GB(Usablespace)
05
1015202530354045
%Througput
Increase
Read+WriteMix
%ThroughputIncreaseforRAID10OverRAID5
%MBPsIncreaseforRAID10
overRAID5
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TestCasesTodeterminethecosttradeoff,twoseparateRAIDgroupswerecreatedwithRAID10andRAID5layout.
ForbothRAID10andRAID5RAIDgroups,theusablespacewasdetermined.Thepercentageofspace
gainedforRAID10comparedtoRAID5wascalculatedfortheanalysis.
Theabovestepswererepeatedforsetsoffour,eight,and16disks,andthetrendanalysiswasdonefor
thecosttradeoff.
ResultsandAnalysisThefollowingtableoutlinesthedetailsofusablespaceforRAID10andRAID5implementationswith
differentsetsofdisks.
No.of
Disks
DiskSize
(GB)
TotalCapacity
(GB)
RAID5UsableSpace
(GB)
RAID10UsableSpace
(GB)
4 300 1073 805 536
8 300 2147 1878 1073
16 300 4294 4025 2146
TableLegendDisksNumberofdisksusedintheRAIDconfiguration
TotalCapacityRawdiskcapacity(diskcapacitynumberofdisks)
RAID5UsableSpaceUsablediskspaceaftercreatingRAID5
RAID10UsableSpaceUsablediskspaceaftercreatingRAID10
Figure6providesthedatafortheusablespace(forbothRAID10andRAID5)thatthecustomercan
achievebyincreasingthenumberofdisks.Figure7depictsthetrendofincreaseinusablespacefor
RAID5overRAID10whenincreasingthenumberofdiskdrives.
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Figure6:UsableSpaceAnalysisRAID10ComparedtoRAID5
Figure7:UsableSpaceGainforRAID5overRAID10
ComparingFigures6and7,theusablespaceforRAID5configurationsissignificantlyhigherthanforthe
RAID10configurations.UsablespaceforRAID5increasesfurtherwhenincreasingthenumberofdisks
usedintheRAIDlayout.Henceforcustomerswhosedatabaseperformanceisnotparamount,optingfor
RAID5deploymentsisavalidtradeoff.AlthoughRAID10oftenoutperformsRAID5inreadandwrite
workloads,RAID5maymatchtheRAID10performanceincaseswheretheapplicationisreadintensive
0
500
1000
1500
2000
25003000
3500
4000
4500
4 8 16
Usable
Space(GB)
Numberofdisks
UsableSpace RAID10ComparedtoRAID5
RAID5_UsableSpace
RAID10_UsableSpace
0
20
40
60
80
100
4 8 16
%Usable
SpaceGain
Numberofdisks
%UsableSpaceGainforRAID5OverRAID10
%UsableSpaceGainforRAID5
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orwithminimalwrite.Insuchcases,RAID5providescustomerswithagreatercostbenefitthanthe
moreexpensiveRAID10option.
AvailabilityTradeoffRAID10ComparedtoRAID5ThissectionexaminestheavailabilityanalysisforRAID10andRAID5implementations,providingan
estimateonhowlongthesystemmaytaketorecoverorrebuildthedataintheeventofadiskfailure.
TestConfigurationsTwoOracle11gR1(11.1.0.7)twonodeRACclustersweredeployed.OneRACclusterwasdeployedwith
aRAID10layoutandtheotherclusterwasdeployedwithaRAID5layout.Thehardwareandsoftware
componentsforthetestwereidenticaltotheperformancetradeofftest.
Thedifferencewasthewaythediskswerelaidoutforthedatabase.Eightphysicaldiskswereusedfor
theRAID10configurationandfivephysicalspindleswereusedfortheRAID5configuration.Wewere
abletocreatethesameamountofusablespacewitheightdisksforRAID10configurationsandfive
disksforRAID5configurations.Theintentwastoloadsameamountofdataforbothconfigurationsand
tomonitortheamountoftimeittakesforthesystemtorecoverfromadiskfailure.
TestCasesTodeterminehowthesystembehavesandrecoversincaseofadiskfailure,bothdatabaseswere
loadedwith400GBofdata.ThentheTPCCtransactionwasstartedforbothdatabasesusingQuest
BenchmarkFactory.Whilethetransactionswereinprogress,onediskwasremovedfromeach
configurationandthedatarebuildtimewasmonitoredforboththeconfigurations.
ResultsandAnalysisTheNavisphereGUIprovidesrealtimemonitoringofthedatarebuildprocess.Afterremovingonedisk
drive,thedatarebuildingwasmonitoredforboththeRAID10configurationandtheRAID5
configuration.ThefollowingtableshowsthepercentageoflongerrebuildtimeforRAID5comparedto
RAID10,takenbythearrayduringdatarebuildprocess.Itneedstobenotedthatthesetestswere
performedwiththeRebuildPrioritysettoHIGH.
Rebuild(%) %LongerRebuildTimeforRAID5ComparedtoRAID10
0
0%
10 35%
20 37%
30 25%
40 20%
50 20%
60 18%
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70 18%
80 20%
90 20%
100 24%
TheRAID10configurationcanrecoverfasterthantheRAID5configuration.FortheRAID10
configuration,thedatawasspreadacrossalleightdisks,andthenthedatasetwasmirrored.Forthe
RAID5configuration,thedatawasspreadacrossallfivediskswiththeparity.Theabovedatarebuilding
trendisexpectedbecausetheparitycalculationfordatarebuildwithRAID5takesmoretime.Fromthe
tableabove,wecanseethatdatarebuildingwithRAID10maybe18%to37%fastercomparedtothat
oftheRAID5configurationintheeventofasinglediskfailure.
Bothofthesedatarebuildingtasksarenondestructiveinnature.TheTPCCrunscontinuedtorun
duringthisrebuildingprocess,buttheperformanceimpactwasnotanalyzedduringthisdatarebuilding
process.
OneimportantavailabilitydifferencebetweentheRAID10andRAID5configurationsisthattheRAID10
configurationcansurvivemorethanonediskfailure,whereasRAID5cantolerateonlyasingledisk
failure.WithaRAID10configurationwitheightphysicaldisks,thesystemcansurvivewithasmanyas
fourdiskfailures(withoutanydataloss),whereaswithaRAID5configurationwitheightdisks,the
systemcansurvivewithonlyonediskfailure,inotherwords,RAID5cannotrebuildthedatawithparity
whenmorethanonediskfails.
FourQuadrantAnalysisThefourquadrantanalysiscanbeusedtodeterminetherecommendedRAIDfordifferenttypesof
workloadsanddatabasesizes.Thisanalysisisparticularlyusefulfordatabaseswithmixeduse
deployment,wherecustomersrunOLTPduringthedayandDSSworkloadatnight.Inthebelowchart,
theXaxisrepresentsthedatabasesize,andtheYaxisrepresentsthetypeofworkload.Thedatabase
sizecanvaryfromsmalltolarge.Theworkloadcanvaryfrom100%OLTPto100%DSS.Thecombination
ofdatabasesizeandworkloadwilldecideintowhichquadrantthecustomerrequirementfalls.For
example,inthecaseofalargedatabasesizewith100%OLTPworkload,therequirementfallsintoQ1.
Basedonourfindings,Figure8providestherecommendedRAIDtypesfordifferentquadrants.
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Figure8:FourQuadrantAnalysisRAIDRecommendationforMixedUseDatabaseDeployments
Quadrant1:LargeDatabaseSizeandOLTPWorkload
Performanceandnondegradeuptimearethekeyconsiderationsinthisquadrant.Aswediscussed
earlier,RAID10isalwaysthebestoptionforthisquadrant.
Quadrant2:SmallDatabaseSizeandOLTPWorkload
Performanceandnondegradeduptimearethekeyconsiderationsinthisquadrantaswell.Becauseof
thesmalldatabasesize,thecustomermaynotreallyhaveahugecostbenefitifchoosingRAID5.For
thisquadrant,althoughRAID5canworkfineforthecustomer,RAID10isrecommended.
Quadrant3:SmallDatabaseSizeandDSSWorkload
Becauseofthesmalldatabasesize,thecustomermaynothavealargecostbenefitifchoosingRAID5.
Forthisquadrant,althoughRAID5canworkfineforthecustomer,RAID10isrecommended.
Quadrant4:LargeDatabaseSizeandDSSWorkload
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ForDSSworkloads,themajordisadvantageistheperformancebottleneckindataloading.Mostofthe
time,thecustomerhasalimitedwindowtocompletethedataloading.Ifthedataloadingactivityfits
intotheallocatedwindow,RAID5canbebestfitforthisquadrant.
ARAIDtyperecommendationforQuadrant4needsfurtheranalysis,becausetheDSSworkloadcanbea
mixofreadandwriteactivities.Foramixeddatabaseusagescenario,databasesareusedforread
intensivequeriesduringdaytimeandforwriteintensivedataloadatnight.TheDSSdataloadactivity
canvaryfromlighttoheavy.Figure9depictstheRAIDtyperecommendationsfordifferentreadand
writeworkloadmixes.TheXaxisrepresentsthedatabasesize,andtheYaxisrepresentstheworkload
mix.
Figure9:RAIDRecommendationforReadandWriteDSSWorkloadMixes
Themajorconsiderationwhendesigningthedatabaseformixeduseisthewindowfordataload.The
dataloadshouldbecompletedwithinthetimespecified,sothatitdoesnotimpactthedatabaseread
operations.Inotherwords,theRAIDconfigurationshouldbeabletomeettheDSSdataloading
performancerequirements.Tobeabletomeettheseperformancerequirements,Figure9canbe
analyzedasfollows:
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1. Forreadintensivedatabaseswithlightdataloadactivities(Q1andQ2inFigure9),RAID5is
recommendedforbothsmallandlargedatabasesizes.RAID5doesnotcreateanyperformance
bottlenecksbecauseofthelightdataloadingactivities.RAID5isahighlycosteffectivesolution
inthiscase.
2. Forsmalldatabaseswithheavydataloadactivities(Q3inFigure9),RAID10isrecommended.
RAID5maybeaperformancebottleneckinthisworkloadscenario.Becauseofthesmall
databasesize,RAID5maynotresultinsignificantcostsavings.
3. Forlargedatabaseswithheavydataloadactivities(Q4inFigure9),RAID10isrecommended.
Forverylargedatabases,theRAID10solutionwillrequiresignificantlymorestorageandwillbe
anexpensivesolution.Inthatcase,thedecisionforwhichRAIDtypetoselectshouldbedriven
bytheamountofwindowavailablefordataloading.
ConclusionConsideringallanalysesfromtheprevioussections,itcanbeconcludedthatRAID5imposes
performancepenaltiesforwriteintensiveworkloads.Theperformancepenaltyincreasesasthenumber
ofwritesincreases.Thisparityoverheadmaycausecontentionforthereadoperation,andthis
cascadingeffectmaydecreasethereadperformance.Henceforallwriteintensiveworkloads,RAID10is
alwaysrecommendedtoachieveoptimumperformance.
Forreadintensiveworkloads,RAID5performancecanmatchthatofRAID10.AsRAID5configurations
providelowcostperGB,itisrecommendedtohavetheRAID5layoutforreadintensiveworkloads.
However,mostoftheOracledatabasesactivitiesarewriteintensive.Thefollowingdatabaseoperations
typicallyexperiencehighwriteactivities
WritingtoOracleControlFiles
WritingtoOnlineredologs
Writingtotemptablespaces
WritingtoUndotablespaces
Performancerequirementsfortheaboveactivitiesareveryhighfromadatabaseperspective.Hence
fromadatabaseenginepointofview,itishighlyrecommendedtoplacetheOraclecontrolfiles,online
redologfiles,temp,andundotablespacesinaRAID10layout.
Databasedatafilesarethetargetfortheuseoftherealapplication.Dependingontheapplication
workload,thecustomershoulddecidetoplacethedatafilesinaRAID10oraRAID5layout.
Basedontheresultsofthetesting,forOLTPworkloadswithahigherwritetoreadratio,itis
recommendedtoselectaRAID10layout.However,acustomercanoptforaRAID5deploymenttohave
acosteffectivesolution.Inaddition,RAID5canbeusedforalightlyloadeddatabasewithoutmuch
performanceimpact.
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ButforwriteintensiveOLAPworkloads(forexample,databasebatchloading),RAID10isstrongly
recommendedforbetterperformance.FordatawarehouseDSSapplicationswithhighlyreadintensive
workloads,RAID5canprovideverygoodperformanceasRAID10and,atthesametime,canbevery
costeffective.Theaboverecommendationsareconsolidatedinthebelowtable:
OracleDatabase
ComponentsWorkloadType Recommended
RAIDConfigurationComments
Controlfiles Writeintensive RAID10 RAID5isnotrecommended.
Redologfiles Writeintensive RAID10 RAID5isnotrecommended.
Undotablespace Writeintensive RAID10 RAID5isnotrecommended.
Temptablespace Writeintensive RAID10 RAID5isnotrecommended.
Datafiles OLTP(higherread
towriteratio)
RAID10/RAID5 Withanincreasingwrite
percentage,RAID5performance
decreases.
Datafiles DSSwrite
intensive
RAID10 RAID5isnotrecommended.
Datafiles DSSread
intensiveRAID10/RAID5 RAID5canmatchRAID10
performance.
Toconclude,RAID10deliversanoptimalperformanceformostdatabaseworkloads.However,RAID5
performancecanmatchtheRAID10performanceforreadintensiveworkloadsorlightlyloaded
databaseworkloads.TheimplementationofRAID5alwaysdeliverslowercostperGB,resultingina
morecosteffectivesolution.Overall,RAID5canperformaswellasRAID10forreadintensive
workloads.
Apartfromtheperformanceandcostanalysis,thecustomershouldalsoconsidertheavailability
perspectiveofthestoragelayout.Asdiscussedearlier,RAID10cansustainmorediskfailures(halfofthe
amountofdisksusedfortheRAIDconfiguration)withnodataloss,whereasRAID5cansustainonlyone
diskfailure.ItshouldalsobekeptinmindthatthehighertheamountofdisksinaRAID5group,the
moretimeisneededtorebuildthedatainthecaseofdiskfailure.
GLOSSARYRAIDRedundantArrayofIndependentDisk.Thetechnologyisusedtoimproveperformanceand
availabilityoftheunderlyingstoragearraysforanyapplication.
OLTPOnlineTransactionProcessingsystemswhicharecharacterizedbyashortresponsetime,small
transactions,andhighconcurrency.Theyusuallyhavehighperformancerequirements.
DSSDecisionSupportSystemssupportbusinessandorganizationaldecisionmakingactivities,and
usuallyhavehighthroughputrequirements.
TPSTransactionsperSecondindicatesthetransactionratethatasystemcansupport.
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ResponseTimeIndicatesthetimeelapsedfortheSQLroundtrip.
ThroughputMeasuresthetrafficflowbetweenthestoragedeviceandtheapplicationservers.
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