TECHNICAL NOTE

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VMware Infrastructure 3

SAN Conceptual and Design Basics

VMwareESXServercanbeusedinconjunctionwithaSAN(storageareanetwork),aspecializedhighspeednetworkthatconnectscomputersystemstohighperformancestoragesubsystems.UsingESXServertogetherwithaSANprovidesextrastorageforconsolidation,improvesreliability,andhelpswithdisasterrecovery.

TouseESXServereffectivelywithaSAN,youreexpectedtobefamiliarwiththeSANtechnology.ThiswhitepaperoffersabriefintroductiontosomebasicSANconcepts,butdoesntaimtobeanexhaustivesourceofinformationonSANs.IfyouareanESXServeradministratorplanningtosetupESXServerhoststoworkwithSANs,youshouldalsoconsultotherresourcesavailableinprintandontheInternettoachieveaworkingknowledgeofSANconcepts.AdditionalinformationonhowESXServerinteractswithSANmaybefoundinSANConfigurationGuide.

Thewhitepaperdiscussesthesetopics:

! SANBasicsonpage 1

! SANComponentsonpage 4

! UnderstandingSANInteractionsonpage 7

! SANInstallationConsiderationsonpage 10

! SANDesignBasicsonpage 11

SAN BasicsASANisaspecializedhighspeednetworkofstoragedevicesandswitchesconnectedtocomputersystems.Thiswhitepaperreferstothecomputersystemsasserversorhosts.

ASANpresentssharedpoolsofstoragedevicestomultipleservers.Eachservercanaccessthestorageasifitweredirectlyattachedtothatserver.ASANsupportscentralizedstoragemanagement.SANsmakeitpossibletomovedatabetweenvariousstoragedevices,sharedatabetweenmultipleservers,andbackupandrestoredatarapidlyandefficiently.Inaddition,aproperlyconfiguredSANfacilitatesbothdisasterrecoveryandhighavailability.

SAN Conceptual and Design Basics

2VMware, Inc.

ThephysicalcomponentsofaSANcanbegroupedinasinglerackordatacenterorconnectedoverlongdistances.ThismakesaSANafeasiblesolutionforbusinessesofanysize:theSANcangroweasilywiththebusinessitsupports.

SAN Component OverviewThissectiongivesanoverviewofSANcomponents.ThenumbersinthetextcorrespondtonumbersinFigure 1,SANComponents,onpage 3.

Initssimplestform,aSANconsistsofoneormoreservers(1)attachedtoastoragearray(2)usingoneormoreSANswitches.Eachservermighthostnumerousapplicationsthatrequirededicatedstorageforapplicationsprocessing.

Thefollowingcomponents,discussedinmoredetailinSANComponentsonpage 4areinvolved:

! SANSwitches(3)SANswitchesconnectvariouselementsoftheSAN.Inparticular,theymightconnecthoststostoragearrays.SANswitchesalsoallowadministratorstosetuppathredundancyintheeventofapathfailurefromhostservertoswitchorfromstoragearraytoswitch.

! Fabric(4)TheSANfabricistheactualnetworkportionoftheSAN.WhenoneormoreSANswitchesareconnected,afabriciscreated.TheFCprotocolisusedtocommunicateovertheentirenetwork.ASANcanconsistofmultipleinterconnectedfabrics.EvenasimpleSANoftenconsistsoftwofabricsforredundancy.

SAN Conceptual and Design Basics

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! Connections:HostBusAdapters(5)andStorageProcessors(6)HostserversandstoragesystemsareconnectedtotheSANfabricthroughportsinthefabric.

! AhostconnectstoafabricportthroughanHBA.

! Storagedevicesconnecttofabricportsthroughtheirstorageprocessors.

Figure 1. SAN Components

How a SAN WorksTheSANcomponentsinteractasfollows:

1 WhenahostwantstoaccessastoragedeviceontheSAN,itsendsoutablockbasedaccessrequestforthestoragedevice.

2 SCSIcommandsareencapsulatedintoFCpackets.TherequestisacceptedbytheHBAforthathostandisconvertedfromitsbinarydataformtotheopticalformrequiredfortransmissiononthefiberopticcable.

3 Atthesametime,therequestispackagedaccordingtotherulesoftheFCprotocol.

4 TheHBAtransmitstherequesttotheSAN.

5 DependingonwhichportisusedbytheHBAtoconnecttothefabric,oneoftheSANswitchesreceivestherequestandsendsittothestorageprocessor,whichsendsitontothestoragedevice.

TheremainingsectionsofthiswhitepaperprovideadditionalinformationaboutthecomponentsoftheSANandhowtheyinteroperate.Thesesectionsalsopresentgeneralinformationonconfigurationoptionsanddesignconsiderations.

ESXServer

storage array

SAN switch SAN switch

fabric A

HBA 2 HBA 1

fabric B

SP SP

1

5

3 3

2

6

4 4

SAN Conceptual and Design Basics

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SAN ComponentsThecomponentsofanFCSANcanbegroupedasfollowsandarediscussedbelow:

! HostComponentsonpage 4

! FabricComponentsonpage 5

! StorageComponentsonpage 5

Figure 2showstheSANcomponentlayers.

Figure 2. SAN Component Layers

Host ComponentsThehostcomponentsofaSANconsistoftheserversthemselvesandthecomponentsthatenabletheserverstobephysicallyconnectedtotheSAN.

! HBAsarelocatedintheservers,alongwithacomponentthatperformsdigitaltoopticalsignalconversion.EachhostconnectstothefabricportsthroughitsHBAs.

! HBAdriversrunningontheserversenabletheserversoperatingsystemstocommunicatewiththeHBA.

ESXServer

ESXServer

storage array

hostcomponents

fabriccomponents

storagecomponents

SP SP

storage array

SP SP

SAN switch A SAN switch B

HBA HBA HBA HBA

fabric Bfabric A

SAN Conceptual and Design Basics

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Fabric ComponentsAllhostsconnecttothestoragedevicesontheSANthroughtheSANfabric.ThenetworkportionoftheSANconsistsofthefollowingfabriccomponents:

! SANSwitchesSANswitchescanconnecttoservers,storagedevices,andotherswitches,andthusprovidetheconnectionpointsfortheSANfabric.ThetypeofSANswitch,itsdesignfeatures,anditsportcapacityallcontributetoitsoverallcapacity,performance,andfaulttolerance.Thenumberofswitches,typesofswitches,andmannerinwhichtheswitchesareinterconnecteddefinethefabrictopology.

! ForsmallerSANs,thestandardSANswitches(calledmodularswitches)cantypicallysupport16or24ports(thoughsome32portmodularswitchesarebecomingavailable).Sometimesmodularswitchesareinterconnectedtocreateafaulttolerantfabric.

! ForlargerSANfabrics,directorclassswitchesprovidealargerportcapacity(64to128portsperswitch)andbuiltinfaulttolerance.

! DataRoutersDataroutersareintelligentbridgesbetweenSCSIdevicesandFCdevicesintheSAN.ServersintheSANcanaccessSCSIdiskortapedevicesintheSANthroughthedataroutersinthefabriclayer.

! CablesSANcablesareusuallyspecialfiberopticcablesthatareusedtoconnectallofthefabriccomponents.ThetypeofSANcableandthefiberopticsignaldeterminethemaximumdistancesbetweenSANcomponentsandcontributetothetotalbandwidthratingoftheSAN.

! CommunicationsProtocolFabriccomponentscommunicateusingtheFCcommunicationsprotocol.FCisthestorageinterfaceprotocolusedformostoftodaysSANs.FCwasdevelopedasaprotocolfortransferringdatabetweentwoportsonaserialI/Obuscableathighspeeds.FCsupportspointtopoint,arbitratedloop,andswitchedfabrictopologies.SwitchedfabrictopologyisthebasisformostcurrentSANs.

Storage ComponentsThestoragecomponentsofaSANarethestoragearrays.Storagearraysincludestorageprocessors(SPs).TheSPsarethefrontendofthestoragearray.SPscommunicatewiththediskarray(whichincludesallthedisksinthestoragearray)andprovidetheRAID/LUNfunctionality.

Storage ProcessorsSPsprovidefrontsidehostattachmentstothestoragedevicesfromtheservers,eitherdirectlyorthroughaswitch.TheserverHBAsmustconformtotheprotocolsupportedbythestorageprocessor.Inmostcases,thisistheFCprotocol.

SAN Conceptual and Design Basics

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Storageprocessorsprovideinternalaccesstothedrives,whichcanbeusingaswitchorbusarchitecture.Inhighendstoragesystems,drivesarenormallyconnectedinloops.ThisbackendlooptechnologyemployedbytheSPprovidesseveralbenefits:

! Highspeedaccesstothedrives

! Abilitytoaddmoredrivestotheloop

! Redundantaccesstoasingledrivefrommultipleloops(whendrivesaredualportedandattachedtotwoloops)

Storage Devices Dataisstoredondiskarraysortapedevices(orboth).

DiskarraysaregroupsofmultiplediskdevicesandarethetypicalSANdiskstoragedevice.Theycanvarygreatlyindesign,capacity,performance,andotherfeatures.

Storagearraysrarelyprovidehostsdirectaccesstoindividualdrives.Instead,thestoragearrayusesRAID(RedundantArrayofIndependentDrives)technologytogroupasetofdrives.RAIDusesindependentdrivestoprovidecapacity,performance,andredundancy.Usingspecializedalgorithms,severaldrivesaregroupedtoprovidecommonpooledstorage.TheseRAIDalgorithms,commonlyknownasRAIDlevels,definethecharacteristicsoftheparticulargrouping.

InsimplesystemsthatprovideRAIDcapability,aRAIDgroupisequivalenttoasingleLUN.ALUNisasingleunitofstorage.Dependingonthehostsystemenvironment,aLUNisalsoknownasavolumeoralogicaldrive.FromaVIClient,aLUNlookslikeanyotherstorageunitavailableforaccess.

Inadvancedstoragearrays,RAIDgroupscanhaveoneormoreLUNscreatedforaccessbyoneormoreservers.TheabilitytocreatemorethanoneLUNfromasingleRAIDgroupprovidesfinegranularitytothestoragecreationprocess.YouarenotlimitedtothetotalcapacityoftheentireRAIDgroupforasingleLUN.

Moststoragearraysprovideadditionaldataprotectionandreplicationfeaturessuchassnapshots,internalcopies,andremotemirroring.

! AsnapshotisapointintimecopyofaLUN.Snapshotsareusedasbackupsourcesfortheoverallbackupproceduresdefinedforthestoragearray.

! InternalcopiesallowdatamovementfromoneLUNtoanotherforanadditionalcopyfortesting.

! RemotemirroringprovidesconstantsynchronizationbetweenLUNsononestoragearrayandasecond,independent(usuallyremote)storagearrayfordisasterrecovery.

Note ASANadministratormustbefamiliarwiththedifferentRAIDlevelsandunderstandhowtomanagethem.Discussionofthosetopicsisbeyondthescopeofthisdocument.

SAN Conceptual and Design Basics

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Tape Storage DevicesTapestoragedevicesarepartoftheSANbackupcapabilitiesandprocesses.

! SmallerSANsmightusehighcapacitytapedrives.Thesetapedrivesvaryintheirtransferratesandstoragecapacities.Ahighcapacitytapedrivemightexistasastandalonedrive,oritmightbepartofatapelibrary.

! Typically,alargeSAN,oraSANwithcritical