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Storage array



Introduction

Storagearray:composedofalargenumberofstorageunits,eachstorageunitcanstore1bitofbinarydata(0,1).UsuallythememorycellsarearrangedinamatrixofNrows×Mcolumns.

Itcombinesmultipledisksintoanarrayandusesthemasasingledisk.Itstoresdataindifferentdisksinastripingmanner.Whenaccessingdata,therelateddatainthearrayisThedisksworktogethertogreatlyreducethedataaccesstimeandatthesametimehavebetterspaceutilization.ThedifferenttechnologiesusedbydiskarraysarecalledRAIDlevels.Differentlevelsareaimedatdifferentsystemsandapplicationstosolvedatasecurityissues.

Generally,high-performancediskarraysareachievedintheformofhardware.Further,diskcachecontrolanddiskarraysarecombinedonacontroller(RAIDControler)orcontrolcardtosolvedifferentusers.Peoplehavefourmajorrequirementsfordiskinput/outputsystems:1)Increaseaccessspeed

2)Faulttolerance,thatis,safety

3)Effectiveuseofdiskspace

4)TrytobalancetheperformancedifferencesofCPU,memoryanddisk,andimprovetheoverallperformanceofthecomputer.

Extendstoragearraylife

InthevSphereenvironment,theadministratorcanuseSSDtoimprovetheperformanceoftheworkload,butyouneedtoknowtherequirementsofyourworkloadtopreventwasteofexpenditure.

SSDischangingstorage.Thecombinationoftheirlowlatency,highthroughput,andmoderateprice,usingSSDasafront-endlargercachehasproducedaseriesofsolutions,whicharecheapbutslow.

OneofthebiggestcharacteristicsofSSDsisthattheirreadandwritespeedscanbewithintensofmicroseconds,whichishundredsoftimesfasterthanordinaryharddrives.ThislowlatencymakesSSDagreatcachingtechnology.

Expensivechoice

Althoughthepricecontinuestofall,SSDwithlowlatencyandhighthroughputisstillahighpricepergigabyte.price.Howtousethisexpensivetypeofstoragecost-effectivelyrequiresyoutohaveknowledgeoftheworkload.Itisimportanttohaveenoughexpensivecachetosupportapplicationperformance.Ifalargercachedoesnotprovideimprovedapplicationperformance,itisawasteofmoney.Therealproblemisthatthereareseveraltoolsthatcanbeusedtoidentifythediskcachesizeofyourapplication.

Inthehistoryofstorage,moststoragearraysusedharddisksasstoragecapacity,combiningalargenumberofharddiskswithsomeRAMthatimprovesperformance.Recently,wehaveseenanemergingeconomicalall-flashstoragearray—noharddrivesinthearray—providinghigherperformancethandiskstorageatthesameprice.Thishaschallengedthediskstoragethatmanycustomershavepurchasedinrecentyears.

Getthemostprofitfromthearray

Thepurchasecycleofstoragearraysislong,generally3-5years.Customerswanttogetbetterperformancefromtheirdiskarraysinamoreeconomicalway,sotheycanavoidprematurereplacements.DiskarrayvendorsaddSSDsasacachefortheperformancelayeroftheirdiskarraystoincreasetheavailableRAM.Accessingdataattheperformancelayerismuchfasterthanaccessingdataatthedisklayer.AdjustingthesizeofSSDcacheandRAMonyourstoragearrayisanewartofoptimizingstorage.

Theconceptofcentralcachereferstothesizeoftheworkingset.Applicationsusuallyaccessasmallpartoftheirdatamuchmorefrequentlythantherestofthedata.Tounderstandthis,thinkofitasanencyclopedia:readingeachpagehasanindexhundredsoftimesmorethanreadinganyotherpage.Havingacomprehensiveindexthatcanbeimprovedbyhundredsoftimeswillbeveryprofitable.Whileotherremainingpagescanbeimprovedbyhundredsoftimes,thereislittlebenefit.

Theobjectsinthestoragearrayareroughlythesame.Asmallpartofdataiscalledhotdata,whichisdatathatisaccessedmorefrequentlythanotherdata.Therealbenefitsofcachingcanonlyberealizedwhenwehaveenoughcapacitytoaccommodateallfrequentlyaccessedpages.Ifthereare10pagesofhotdata,andthecachecanonlyhold5pages,thenwemustwaittoretrievetheother5pagesontheslowermedia.Itwouldbehelpfultohaveenoughcachetostoresomenormalpages,butnotasfastasthecachedindex.

Calculatetheappropriatecachesize

WhentheSSDcachecansupportthesetapplicationdataworkingsetisthemostvaluable.FailuretoprovideenoughSSDsfortheworkingsetwillnotprovidethebestperformance.Supposeanapplicationhas500GBofdata.Iftheapplication'sI/Ois40%andonly20GBofdataisused,thenobviouslyhavinga20GBcachewillbeagoodimprovement.Itisalsoagoodchoicetoincrease40%ofI/Obyahundredfold.Soifa100GBcachecanprovidebetterperformance?Itispossible,butnotnecessarily.Maybethenext40%oftheapplication'sI/Owilltransferdataupto200GB.However,increasingto100GBwillnotprovidethesamelevelofimprovementasthefirst20GB.Theadditional80GBcachemayspeeduptheI/Oofonly15%ofapplications,andwillcostfourtimestheinitialimprovement.

Challengehotdata

Thebiggestchallengeisthattheamountofhotdataisdifficulttomeasure.Evenforspecificapplicationtypes,applicationsfordifferentpurposes—differentusers—willhavedifferentprofiles.

Therearealsomultiplelevelsofhotspots.Theencyclopedia,thetableofcontentsissmallbutusesmorethanindexes.Andtheindexisverylargeandsetlargeonallpages.Ifthereisaseriesoflargecachesthosewillbehelped;ifthecacheislarger,therewillbeaseriesoflevelsofperformanceimprovement.Therearealsoaseriesofthesamelevelthatdoesnotimproveperformanceasthecacheincreases.IfyourperformancelayerisSSD,whichisveryexpensive,thenyouneedtomeasureyourworkloadandpurchasetherightamountaccordingtoyourworkload.

All-flashstoragearrays

Theemergenceofthecloudhasmadevirtualizationofmanyworkloads,includingdesktops,areality.ButnowITprofessionalsareclamoringforfasternetworkstorage.All-flasharraystoragearrayistheFerrariofstorage.Storagearrayscandeliverhighperformanceandarereadytotriggerarevolutioninthestoragefieldbyeliminatingmechanicalharddrives.Networkstoragearraysfaceaseriesofchallenges.Whenauserstartsavirtualdesktop,thenetworkstoragearraymustdelivertheOSstackandapplicationsrequiredbytheinstance.Ideally,thiswillbedoneimmediately.Butsomanynewinstancesappearinbatches—especiallyinvirtualdesktopenvironments—sometimesitfeelslikebootingfromafloppydisk.

Howcanall-flashstoragearrayshelp?

All-flashstoragearrayscanwithstandbootstormsandsolvemanyothervirtualizationperformanceissues.Althoughstoragearrayequipmentisexpensive,itdeliversthebestperformanceintermsofunitcost.Storagearraysvaryinsize,andmedium-capacitystoragearrayscanstorealargenumberofdesktopmirroringconfigurations,andallowITtobootthousandsofVDIinstancesperhour,almostasfastaslocalstorage.Therapidexpansionoflarge-capacityunitshasbroughtanotherpotentialusecaseforall-flashstoragearraystorage:thetop-levelnetworkstoragearrayforstoringbigdata.In-memorydatabaseenginesandGPU-basedsystemshavehighI/Orequirements.IfthenetworkI/Osystemfailstomeettherequirements,itislikelythatperformancewillfallintoabottleneck.PB-levelall-flashstoragearrayscanprovidethelargecapacityrequiredforbigdata,andcanalsomeetthedeliveryefficiencyrequirements.PB-levelarraycostsarealsoacceptable,becausethestoragearrayprovidesback-enddeduplication,andtheoriginalcostislessthan$2/GB.Theretailpriceofall-flashstoragearraysisalsoconstantlyimproving.Theemergenceof3DNANDflashmemorywillcauseitspricetofallfurthernextyear,furtherexpandingthedifferencebetweentheall-flashstoragearrayandtheoldmechanicaldiskarray.Thecontinuedimprovementoftechnologyisworthlookingforwardto,andthepriceofall-flashstoragearrayswillalsobefurtherreduced.

Storagearraycontainersreversethedefeat

Anewwayofthinkingaboutvirtualizationistobereadytosweepthecloudatanytime.Theoldwayofencapsulatingtheoperatingsystemandapplicationstackineachstoragearrayvirtualdesktopmachineresultedinalargenumberofmemorycopiesandexcessivelyhighdynamicrandomaccesstothememory.EverymorningwhenhundredsofcopiesofMicrosoftWindowsandOfficearedeliveredtoavirtualPC,italsocausesabootstorm.Storagearraycontainertechnologyischangingallofthis.Storagearraycontainersarestillintheearlystages,butthestoragearraycontainermodelavoidsinstallingmultipleoperatingsystemsandapplications.Storagearraycontainersonlyneedtouseasinglecopy,butthepriceisreducedflexibility,becauseallvirtualmachinesmustusethesameoperatingsystem,butthousandsofimagesinthecloudarealmostidentical,sothisisnotproblem.Usingstoragearraycontainers,eachserverloadsasingleoperatingsystemimage,whichcanderivehundredsofvirtualstoragearraydesktops,achievinghigherinstancedensityatalowercost,andstoragearrayscanalsobenefitfromreducedbootimagetraffic.Evenso,theuseofall-flashstoragearraysasthefirst-levelstoragetierisstillofgreatsignificance,becausethecapacityofatypicalstoragearrayshouldgrowtothepetabytescale.Somemanufacturerswillhavetoadjusttheirproductpositioning,butmanufacturersthatsupplylow-cost3DNANDflashmemoryproductswillhaveaclearadvantageinthecompetition.

Storagearraysbreakthecompetition

Thetrade-offbetweenstandardSSDsanddedicatedall-flashstoragearraysaddsanothercomplexcombination.Comparedwithall-flashstoragearrays,smalldevicesusingSSDandARMprocessorshavemoreadvantagesinprice.TheriseofSSDsandlocalEthernetinterfacesmayfurtherenhancetheadvantagesoflocaldrives.All-flashstoragearraysarewinningthegame,buttheresultisstillunclear.Competitionislikelytobecomefierce.Ifyouwanttostayahead,all-flashstoragearrayvendorscannotmaintaincurrentpricesorstandstill.Thegoodnewsforusersisthatvirtualdesktopswillbecomefaster,cheaper,andeasiertodeploy,andbootstormswilleventuallybecomehistory.

Application

Astoragearraymayhavedifferentareasfortraditionalharddiskandsolid-stateharddiskdevices.Storagearraysdothissometimestomeetdifferentcoolingrequirementsorpowerdensities.Inappropriatehybriddisktypesinthestoragearraycancauseinterruptionsinairflow,whichcanincreaseheatgenerationandshortendisklife.Diskarrayperformanceislimitedbytheslowestdisk,sotrytoavoidmixingdisksinJBOD.StoragearraysuseasingletypeofharddriveorSSD,ortrytomatchdiskcharacteristics,suchasrotationspeed.Checkthespecificationsofthearraystoragearrayandprohibitanytypeofdiskorcombinationofdisks.

Usestoragearraysthatalreadyhaveacertifiedplatform.Forexample,JBODstoragearraysuseserial-attachedSCSIinterfaceconnectionstoreportthediskstatusofasingledisk/slot.ThestoragearrayallowsadministratorstocheckeachoftheJBODarrays.Theconditionofthedisk.Thiswillspeeduptroubleshooting,andthestoragearraywillallowtechnicianstoquicklyisolateandreplacediskdevices.

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