tradeoffs raid5 raid10

8/6/2019 Tradeoffs RAID5 RAID10

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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.


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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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Page5

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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