Dell Ha Exchange 2007

7/31/2019 Dell Ha Exchange 2007

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August 2007

High Availability inExchange Server 2007

Product Group - Enterprise

Del l Whit e Paper

By

Ananda Sankaran

Mahmoud Ahmadian


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August 2007 Page 2 Dell Product Group - Enterprise

In t roduct ion .................................................................................................................. 3

High Avai labi l i t y for Server Roles in Exc hange 2007 ............................ 4

Mai lbox Server Role Avai labi l i ty Opt ions ..................................................... 6

Single-Copy Clusters ...................................................................................................... 6

Local Continuous Replication ........................................................................................ 7

Cluster Continuous Replication.................................................................................... 10

Comparison................................................................................................................... 14

Avai labi l i t y Opt ions for Other Server Roles .............................................. 16

Hub Transport Server Role Availability....................................................................... 16

Client Access Server Role Availability ........................................................................ 17

Edge Transport Server Role Availability...................................................................... 17

Unified Messaging Server Role Availability................................................................ 17

High Avai labi l i ty Deployment Considerat ions ......................................... 19

Conclusion .................................................................................................................. 20


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I n t roduc t ion

Availabilitycanbecrucialforenterpriseoperationsandisakeycomponentinmeetingreturn

oninvestmenttargets. Enterprisemessagingsystemsdrivecorebusinesscommunications,andit

becomescriticaltoensuretheiravailability.NewhighavailabilityfeaturesbuiltintoMicrosoft

ExchangeServer2007aresignificantimprovementsaimedatprovidingflexibleandcosteffective

dataprotectionandavailabilityoptionsforExchangedeployments.InExchangeServer2003,

nativemailboxavailabilitycapabilitieswerelimitedtosharedstorageclusteringwithMicrosoft

ClusterServices,whichinExchangeServer2007isreferredtoasSingleCopyClusters(SCC).

ExchangeServer2007introducestheadditionalmailboxavailabilityoptionsLocalContinuous

Replication(LCR)andClusterContinuousReplication(CCR).ThisarticlewilldiscussExchange

Server2007highavailabilityfeaturesandassociatedbenefits.Performanceanalysisconductedat

Delllabstocharacterizethebehaviorofmailboxavailabilityoptionswillbediscussed.


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High Avai labi l i t y for Ser ver Roles in

Exc hange 2007

Exchange Server 2007 provides or distributes its features and functionality through the fivedifferent server roles: Mailbox, Hub Transport, Client Access, Edge Transport and Unified

Messaging.Figure1illustratesthedifferentExchangeServer2007rolesinanexampleExchange

Server2007infrastructure.

Figure1:MicrosoftExchangeServer2007Infrastructure

StorageSystems

Fibre ChannelSwitches

MailboxServers

EdgeTransportServers

Internal OutlookClients

Client AccessServers

Active Directoryand GlobalCatalog Servers

Hub TransportServers

External Clients UnifiedMessagingServers

Exchange 2007

Server Roles

InternalTelephones/Fax

External Telephony

Perimeter Network

PSTN PBX/VOIP

Internet


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EachofthefiveserverrolesprovidesdifferentExchangeServer2007functionality.Deploying

eachroleinahighlyavailablemannerensuresavailabilityofitssupportedfunctions.High

availabilityforeachserverrolecanbeprovidedusingbuiltinExchangeServer2007featuresand

otherstandardEnterprisemethodsdependingontheserverrole.Deploymentscanbemadewith

certainserverrolesinahighlyavailableconfigurationandtherestinastandaloneconfiguration.

Forexample,dependingonbusinessandITneeds,thedecisionmaybemadetodeploythe

mailboxserverroleinahighlyavailableconfigurationandtheotherrolesinastandalone

configuration.ThischoicemaybedrivenbyanITdecisionthatmanuallyrecoveringfroma

mailboxserverfailureiscomplexandtimeconsuming,withpotentiallyunacceptabledowntime

comparedwithrecoveringotherserverroles.Nevertheless,deploymentplanningshould

carefullyassesstheavailabilityrequirementsforeachserverrolebasedonthedowntimeSLA

(ServiceLevelAgreement)forthatrolesfunctionalityandassociatedrecoverabilityparameters.

Thechoiceofaparticularavailabilitymethodfordeployingaserverrolewillbefurther

influencedbyvariousotherfactorssuchascost,manageability,andscalability.


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Mai lbox Server Role Avai labi l i t y Opt ions

TheMailboxserverroleisthemostcriticalroleinanExchangedeploymentsinceithoststheuser

mailbox

data.

It

is

crucial

that

the

mailbox

server

application

and

the

data

it

hosts

are

available

andsecure.ExchangeServer2007providesoptionstoachievehighavailabilityforeitherthe

mailboxserverapplicationorthemailboxdataorboth.Deploymentscanemployoneofthese

optionsbasedontheavailabilityneeds.Thethreenativehighavailabilityoptionsavailablefor

theMailboxserverroleinExchangeServer2007aredescribedinthefollowingsections.

Single-Copy Clusters

SingleCopyClusters (SCC)enablehighavailability for themailbox serverapplication.SCC is

basedonthesharedstorageMicrosoftClusterServices(MSCS)clusteringmodelthatexistedwith

previous

Exchange

versions.

It

follows

a

shared

nothing

architecture

wherein

a

single

copy

of

the

storagegroupsanddatabasesresideonsharedexternalstorage.TwoormoreExchangemailbox

serversareconnectedtothissharedstoragetoformacluster.Atanytimeonlyasubsetofthese

servers,calledactivenodes,hostthemailboxdatabasesresidingonthesharedstorage.Ifoneof

theactivenodes incursafailure,anotherserverinthecluster,calledapassivenode,takesover

hostingitsmailboxdatabases.Thisprocessistermedasafailoverandthesetypesofclustersare

alsopopularlycalledfailoverclusters.Comparedwithpreviousversions,ExchangeServer2007

provides improveddeployment setupandmanagementexperiencewith thisclusteringmodel.

EnhancedmanagementtoolsforExchangeServer2007suchastheExchangeManagementShell

allow administrators to manage clustered deployments seamlessly. Deployment support for

Single Copy Clusters requires the configuration to be certified and listed in the Microsoft

WindowsServerCatalogundertheClusterSolutioncategory.DeployingExchangeServer2007

withother

versions

of

Microsoft

Exchange

Server

or

SQL

Server

in

the

same

cluster

is

not

supported.However, deploying SQL Server 2005 Express Edition or otherMicrosoft desktop

databaseapplications (OfficeAccess) issupportedon theclusternodes inastandalone,non

clusteredmode.Windows Server 2003 supports up to eight server nodes in a cluster. It is

recommendedthateachactivemailboxserverintheclusterhaveacorrespondingpassivenode

in the cluster. This isbecause at any time a cluster node can host only one active clustered

mailboxserverand,whenmultipleactivenodefailuresoccur,theremaynotbesufficientpassive

nodestohandlethefailover.


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Figure 2: Dell PowerEdge FE600W Cluster deployment for SCC

IftheMailboxserverroleisdeployedinahighlyavailableclusteredconfigurationusingSCC,no

otherserverrolecanbeconsolidatedwiththeMailboxroleonthesameserver.ThusinSCC

deployments,separateservers,inadditiontothemailboxclusterservers,needtobeprovisioned

fordeployingtheHubTransportandClientAccessroles.SCCensuresavailabilityofonlythe

mailboxapplication.HighavailabilityforotherExchangeserverrolescanbeprovidedthrough

mechanismsdiscussed

in

later

sections.

Local Continuous Replication

LocalContinuousReplication(LCR)providesavailabilityatthedataleveltothemailbox

databases.LCRdoesthisbycreatingandmaintainingacopyoftheExchangestoragegroups

logsanddatabaseonasecondsetofdiskvolumesconnectedtothesamemailboxserver.The

copyismaintainedasynchronouslyusingtransactionlogcopyandreplayonthetarget

databases.Thecopiedversionofthestoragegroupiscalledapassivecopyandthe

correspondingoriginalproductionversioniscalledanactivecopy.Thepassivecopyofthe

storagegroup

is

initially

created

by

copying

from

the

active

storage

group

through

aseeding

process. Subsequentupdatestotheactivestoragegrouparesynchronizedwiththepassive

storagegroupviaalogcopyprocessfromtheactivetothepassive.Thecopiedtransactionlogs

arethenreplayedonthepassivestoragegroupsdatabase.Incaseofanactivecopyfailure,the

mailboxservercanbepointedmanuallytostartusingthepassivecopyastheproductionversion.

LCRprovidesanexcellentoptionforquickrecoveryfromusererrorsanddataleveldisastersthat

causedatabasecorruption.Thepassivedatabasecopiescanbeusedtooffloadtherequired

backupactivitiesfromtheactivedatabaseswithminimalimpacttotheenduserresponsetime.


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Thusthebackupwindowcanpotentiallybeextendedtohandlelargedataduetotheminimal

effectontheactivecopy.Thebackupschedulecanalsobemodifiedtoremovetherequirementof

dailyfullbackupsduetotheavailabilityofpassivecopyandinsteaduseweeklyfullbackups.

AsetofperformancetestswereconductedonaLCRconfigurationasillustratedinFigure3.The

objectivewastounderstandtheperformanceimpactsofenablingLCRonthemailboxserverand

storagesubsystem.SimulationswereconductedontheconfigurationwithLCRdisabledand

enabledonthemailboxserver.Theutilizationlevelsofvarioussystemresourceswererecorded,

andtheiraveragevaluesaredisplayedinFigure4andFigure5.

Figure 3: LCR Test configuration (Source Dell Power Solutions, August 2007)

ConfigurationDetails:Mailboxserver DellPowerEdge2950with2xIntelXeon5160dualcore3.00GHzprocessors;8GB

systemRAM

WindowsServer2003R2Enterprisex64EditionwithSP2;ExchangeServer2007

EnterpriseEditionHubTransport/ClientAccessserver DellPowerEdge2950with2xIntelXeon5160dualcore3.00GHzprocessors;16GB

systemRAM


EnterpriseEditionExternalmailboxstorage 1xDellPowerVaultMD3000with1xDellPowerVaultMD1000attached

Databasevolume:RAID10with10x146GB15KRPMSASdrives(MD3000)


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Logvolume:RAID1with2x146GB15KRPMSASdrives(MD3000)

Databasecopyvolume:RAID10with10x146GB15KRPMSASdrives

(MD1000)

Logcopyvolume:RAID1with2x146GB15KRPMSASdrives(MD1000)MicrosoftLoadgenSimulationTool Buildversion:08.01.0094.000

Userprofile:1000heavyusersexecuting94tasksper8hruserdayinOutlook2007online

mode

AsshowninFigure5,thedatabasediskreadsandwritesandthelogdiskreadsandwritesareat

aboutthesamelevelwhenLCRiseitherdisabledorenabledontheactivecopy.Thepassivecopy

incursfewerdatabasereadsthantheactivecopyduringLCRactivity.Thelogdiskactivityisalso

slightlydistinctbetweenactiveandpassivecopiesduetothelogsbeingreadfromtheactive

copyandreplayedonthepassivecopy.Theservershowsslightlyincreasedutilizationof

processorandmemorywhenLCRisenabled(Figure4).About4%extramemoryand15%extra

CPUisutilizedwithLCRenabled.ThuswithLCRenabledmoreprocessorandmemoryshould

beallocatedtothemailboxserver.

Figure 4: LCR processor and memory utilization levels

LCR-off Vs LCR-on : Processor & Memory

0

2

4

6

8

Memory Utilization (GB) % Processor Utilization

Resources

Ave

rage

value

LCR-off

LCR-on


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Figure 5: LCR database and log I/O generated

Generallyitisrecommendedthatabout20%extraprocessorutilizationbeaccommodatedand

about1to1.5GBextramemorybeallocatedonthemailboxserverforLCR.Thepassivecopy

incursabout25%lessdatabaseI/Osthantheactivecopy.Thenumber,type,andRAID

configurationofdiskdrivesallocatedtothepassivecopyvolumecanbeadjustedforthisfactor.

Ifthepassivecopywillbepromotedtoproductionforsupportingregularscheduled

maintenanceoftheactivecopy,thenitisrecommendedthatthepassivecopybeprovidedthe

samesetofdiskresourcesastheactivecopy.

Cluster Continuous Replication

ClusterContinuousReplication(CCR)enableshighavailabilityofboththemailboxserver

applicationandthemailboxdata.CCRisbasedontheMicrosoftClusterServices(MSCS)

MajorityNodeSet(MNS)model.Thismodeldoesnotrequiresharedstorageandthetwo

mailboxservernodeswithintheclustermaintaintheirowncopyofmailboxdatabases. Atany

timeoneoftheclusterserversactsastheactivenodeandservesclientrequests.Theotherserver

remainsasapassivenodeandautomaticallytakesoveriftheactivenodeincursafailure.CCR

providesautomaticserverfailovercapabilitysimilartoSCC.Athirdserver,calledwitnessfile

share,providesarbitrationandallowsonlyoneservertofunctionasactivenodeatanytime.The

passivecopyofstoragegroupiskeptconsistentwiththeactivecopythroughdatareplication.

Datareplication

is

performed

by

Exchange

Server

at

the

application

level

and

not

by

the

MNS

clusterinfrastructure.Thereplicationtakesplaceintheformofasynchronoustransactionlog

copyandreplay.Thepassivenodecopiesthetransactionlogsoftheactivenodefromasecure

fileshareontheactivenodeandreplaysthemlocallytoupdateitsdatabase.Beforeenabling

CCR,thepassivecopyiscreatedbycopyingtheactivedatabasecopythroughaseedingprocess

toensureconsistency.CCRcanprovidesiteresiliencybydeployingtheactiveandpassivenodes

ingeographicallyseparatedatacenters.CCReliminatestheneedforasharedstorage,andthe

storagespaceallocatedtothedatabaseandlogsonthepassivenodemustbeequalorlargerthan

LCR-off Vs LCR-on : I/O

0100200300400500

DBDisk

Reads/sec

DBDisk

Writes/sec

LogDisk

Reads/sec

LogDisk

Writes/sec

Disk Entities

Averagev

alue

Active Copy (LCR-off)

Active Copy (LCR-on)

Passive Copy (LCR-on)


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thatoftheactivenode.CCRoffersenhancementstodatabackupandrecoverystrategysimilarto

LCR.ThepassivedatabasecopyinCCRcanbeutilizedforoffloadingrequireddatabasebackup

activityandalsotoreducebackupfrequency.

Theclusternodescommunicatewitheachotherabouttheirlivelinessviaprivateheartbeats.

WhenthenodeswithintheCCRclustercannotcommunicatewitheachother,thewitnessfile

shareservesasatiebreakertoavoidsplitbrainscenarioswhereeachnodefunctionsasthe

activenode.ThefilesharewitnessservermustbehostedbyamachinethatisnotpartoftheCCR

clusterbutshouldbepartoftheActiveDirectorydomaincontainingtheclusternodes,anditis

recommendedthatitbetheHubTransportserver.Thefilesharewitnessclusterresourcetypeis

arecentadditionalclusterresourceprovidedinMicrosoftWindowsServer2003ServicePack1.

WindowsServer2003SP1alsoaddedconfigurableclusterheartbeatstoclusterservices.Thisis

especiallysignificantforclusterswhichcouldbedeployedingeographicallydispersedlocations.

Thisfeatureallowsconfigurationofclusterheartbeatparameterssothattemporarynetwork

problemsdonotcauseunnecessaryfailovers.TheHubTransportserverincludesafeaturecalled

TransportDumpsterwhichisutilizedtoavoiddatalossduringfailoveroftheactivemailbox

servernode.TheTransportDumpster,maintainedintheHubTransportserver,isaqueueof

recentlydelivered

messages

to

the

active

mailbox

server

from

clients

and

other

services.

At

the

timeofafailure,theactivemailboxservermaynothavecompletedprocessingtheserecent

messages.Thustoensuretheircompletionafterafailover,allHubTransportserversinthe

ActiveDirectorysitearerequestedtoresubmitthemailintheirTransportDumpsterqueuetothe

newactivemailboxserver.Thisensuresthatallrecentlydeliveredmessagesgetrecordedand

preventsdatalossduringfailures.Certainusecasesorscenariosexistwherethisfeaturedoesnot

providecompleterecoveryfromuserdataloss.

IftheMailboxserverroleisdeployedinaclusteredconfigurationusingCCR,nootherserverrole

canbeconsolidatedwiththeMailboxroleonthesameserver.ThusinCCRdeployments,

separateservers,inadditiontothemailboxclusterservers,needtobeprovisionedfordeploying

theHub

Transport

and

Client

Access

roles.

CCR

ensures

availability

of

only

the

mailbox

applicationandmailboxdata.HighavailabilityforotherExchangeserverrolescanbeprovided

throughmechanismsdiscussedinlatersections.

DuringCCRoperations,workisperformedbythepassivenodetocopylogfilesfromtheactive

nodessecurefileshareandtoreplaythelogstoitsdatabasecopy.Asetofperformancetestswas

conductedonaCCRconfigurationasillustratedinFigure6.Theobjectivewastounderstandthe

performanceimpactsofCCRontheactive/passivemailboxservernodesandtheirassociated

storagesubsystem.SimulationswereconductedontheconfigurationwithCCRdisabledand

enabledontheactivenode.Theutilizationlevelsofvarioussystemresourceswererecorded,and

theiraveragevaluesaredisplayedinFigure7andFigure8.


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Figure 6: CCR Test Configuration (Source Dell Power Solutions, August 2007)

ConfigurationDetails:Mailboxservers(Activeandpassive) DellPowerEdge2950with2xDualCoreIntelXeon51603.00GHzprocessors;8GB

systemRAM


EnterpriseEditionHubTransport/ClientAccessserver Dell

PowerEdge

2900

with

2xQuad

Core

Intel

Xeon

X5355

2.66

GHz

processors;

16

GB

systemRAM


EnterpriseEditionExternalmailboxstorage 1xDellPowerVaultMD1000eachonactiveandpassivenode

Databasevolume:RAID10with10x300GB15KRPMSASdrives(MD1000)

Logvolume:RAID1with2x73GB15KRPMSASdrives(MD1000)

Databasecopyvolume:RAID10with10x146GB15KRPMSASdrives

(MD1000)

Logcopyvolume:RAID1with2x73GB15KRPMSASdrives(MD1000)MicrosoftLoadgenSimulationTool Buildversion:08.01.0094.000

Userprofile:1000heavyusersexecuting94tasksper8houruserdayinOutlook2007

onlinemode

AsshowninFigure8thedatabasereadsandwritesandthelogwritesremainalmostthe

samewhenCCRisdisabledorenabledontheactivenode.Thelogreadsshowaslight


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increaseontheactivenodewhenCCRisenabledduetothelogcopyprocess.Thepassive

nodeshowsincreaseddatabasewriteactivityandlogreadscomparedtotheactivenode.

Thisisduetothecontinuouslogreadandreplayprocesshappeningonthepassivedatabase

copy.TheprocessorandmemoryutilizationremainalmostatthesamelevelswhenCCRis

enabledanddisabledontheactivenodeasshowninFigure7.Theutilizationonthepassive

nodeislowercomparedtotheactivenodeduringCCRactivity

.

Figure 7: CCR processor and memory utilization levels

Figure 8: CCR database and log I/O generated

CCR-off Vs CCR-on : I/O

0100200300400500600

DBD

isk

Reads/sec

DBD

isk

Writes/Sec

LogDisk

Reads/sec

LogDisk

Writes/Sec

Disk Entities

Average

value

Active node (CCR-off)

Active node(CCR-on)

Passive node(CCR-on)

CCR-off Vs CCR-on : Processor & Memory

0

2

4

6

8

% Processor Utilization Memory Utilization (GB)

Resources

Average

value

Active node (CCR-off)

Active node(CCR-on)

Pass ive node(CCR-on)


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Generallybothactiveandpassivenodesshouldbeprovidedwiththesamesetofprocessorand

memoryresourcesforCCR.Therequirementsaresimilartothestandalonemailboxserver

requirementsforagivenuserload.Thepassivenodeshouldbeprovidedwiththesame

processorandmemoryresourcesasactivenode,eventhoughduringCCRactivityit

underutilizesthoseresources.Thisisbecause,afterfailover,thepassivenodeisrequiredtobe

operatedastheactivenodewiththeactualuserload.Theactivenodeincursabout10%extra

databaseI/OsduringCCRactivity,andthisneedstobeconsideredwhiledesigningthestorage

subsystem.Thepassivenodeincursabout40%moredatabaseI/OsthantheactivenodeforCCR.

Thiscanbeconsideredindesigningthestoragesubsystemforthepassivenodetomeettheideal

I/Operformancebestpracticesforthepassivenode.However,sincethepassivenodedoesnot

handletheproductionload,theadditionalI/Orequirementneednotbeconsideredwhile

designingitsstoragesubsystem.Thepassivenodesstoragemayexhibitlessthanoptimal

performancebehavior,whichmaybeacceptableforcertaindeployments.Thistradeoffshouldbe

carefullyassessedtoappropriatelydesignthepassivenodestoragesubsystem.Inmostcases,it

shouldbeprovisionedwithatleastthesamesetofdiskresourcesastheactivenode.

Thenetworkinfrastructurebetweentheactiveandpassivenodesshouldbecarefullyplannedas

well.The

public

network

interface

on

all

cluster

nodes

should

be

on

the

same

subnet.

The

private

networkinterfaceonallclusternodesshouldbeonthesamesubnetaswellbutdifferentfromthe

publicnetworksubnet.VirtualLAN(VLAN)implementationscanbeusedbetweenclusternodes

toovercomegeographicallimitationsimposedbythesubnetrestrictions.However,itmustbe

ensuredthattheclusterprivatenetworkpointtopointroundtriplatencyislessthan0.5seconds.

Theprivateheartbeatnetwork,usedfordeterminingthehealthofclusternodes,shouldbe

capableofsendingandreceivingheartbeatinformationwithinacertainnumberofretrieswhich

isconfigurable.Ifthenodesaredistantfromeachother,thenetworklatencywillbecomea

determiningfactorofhowfastthelogcopyprocessoccursonthepublicnetworkandthe

resultantlagofthepassivecopyfromtheactivecopy.Sufficientnetworkbandwidthshouldbe

accountedbetweenthenodes,especiallyduringtheinitialseedingprocess,whenthedatabaseis

copiedover

the

network

to

the

passive

node.

Also,

very

large

databases

incurring

high

update

activitywillrequireamplebandwidthtocopytheresultantlogsfromtheactivenodetothe

passivenodewithinreasonablelatencylimits. AgigabitEthernetnetworkinfrastructureata

minimumisrecommendedforsuchdeployments,alongwithmechanismssuchasNICteaming

forthepublicnetworkontheclusternodestoensurebandwidth.

Comparison

Figure9providesahighlevelcomparisonofthethreemailboxhighavailabilityfeatures

describedinearliersections.Specificdeploymentrulesapplyfordeployingthesefeatures.

Appropriateproduct

and

feature

documentation

should

be

consulted

before

planning

these

deployments.


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Feature SCC CCR LCR

Availabilitylevel Application ApplicationandData DataAutomaticFailover Yes Yes NoNativeDataReplication No Yes YesSiteResilienceforDisasterRecovery No Yes NoMicrosoft

Windows

Server

Catalog

Listingforclustersolutionhardware Yes No NoBackupimprovements No Yesoffloadto

passivecopyYesoffloadtopassivecopy

Figure 9: Mailbox availability feature comparison

AnewreplicationfeaturecalledStandbyContinuousReplication(SCR)isintroducedwith

ExchangeServer2007ServicePack1.TheSCRfeatureenablesdatareplicationtostandby

recoverymailboxserversthatarenotpartofanMNScluster,providingamoreflexibledata

replicationtopologyoption.AtthetimeofthepublicationofthiswhitepaperExchangeServer

2007SP1wasnotreleased.


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Avai labi l i t y Opt ions for Ot her Ser ver Roles

Itmayberequiredtodeployotherserverrolesinahighlyavailableconfigurationinadditionto

the

Mailbox

server

role.

Availability

for

these

server

roles

can

be

achieved

thorough

a

variety

of

methods.Thefollowingsectionsdescribesomeofthesemethods.

Figure 10: High Availability for server roles

Hub Transport Server Role Availability

HighAvailabilityfortheHubTransportserverrolecanbeprovidedbydeployingmultipleHub

Transport serverswithin the site. Internal transport services on the Exchange server rolesby

defaultworkwithmultiple Hub Transport servers, and additional configuration or external

networkloadbalancingsupportisnotrequired.TheHubTransportserversdeployedinthesite

StorageSystems

Fibre ChannelSwitches

MailboxServers

EdgeTransportServers

Internal OutlookClients

Client AccessServers

Active Directoryand GlobalCatalog Servers

Hub TransportServers

External Clients UnifiedMessagingServers

Exchange 2007Server Roles

InternalTelephones/Fax

External Telephony

Perimeter Network

PSTN PBX/VOIP

Internet

SCC / CCR

DNS RoundRobin / MX

Default HA

Load Balancing

VOIP RoundRobin

HA Method forServer Roles


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areidentifiedthroughtheirconfigurationinformationinActiveDirectorybytransportservices.If

oneof thedeployedservers fails,otherservers inthegroupwillensureavailabilityof theHub

Transportrole.DeploymentscanprovisiontwoormoreHubTransportserverspersitebasedon

theavailabilityandscalabilityneeds.

Client Access Server Role Availability

HighAvailabilityfortheClientAccessserverrolecanbeprovidedbydeployingmultipleClient

Accessserversandusing loadbalancing solutions todistribute the incomingclient requests to

thoseservers. ThenativeWindowsNetworkLoadBalancing (NLB)servicesorstandard third

partyhardware or softwarebased loadbalancing solutions canbeutilized.Deployments can

provisiontwoormoreClientAccessservers,configuredwithaloadbalancingsolution,basedon

theavailabilityandscalabilityneeds.

WindowsNLB Services is includedwithin the appropriateWindows Server 2003Edition and

doesnotmandateothersoftwareorhardwarerequirements.Theserviceneedstobeconfigured

on all the client access servers to form an NLB cluster. The servers in the cluster will be

representedbyasinglevirtualIPaddressandnetworkname.Allclientrequestswillbedirected

to thisvirtualaddress,andoneof theservers in theclusterwillservice theclient request. Ifa

server fails, the remaining servers in the cluster continue providing services ensuring service

availability and scalability.As abest practice, each server can have one network adapter for

participating in theclusterandanothernetworkadapterforany trafficdirectlyaddressedto it.

CertainfeaturesoftheClientAccessrolerequireclientaffinity,whereaseriesofrequestsfroma

client need tobe satisfiedby the same server thatmaintains state and notby other cluster

members.WindowsNLBServicesincludesoptionstoenforcethisaffinity.DNSRoundRobinis

anothermethodusuallyconsideredforloadbalancingclientrequestsacrossmultipleservers. A

listofserver IPaddresses ismaintainedat theDNSandclient requestsare resolved tooneof

theseIP

addresses

by

going

through

the

list

in

aRound

Robin

fashion.

DNS

Round

Robin

cannot

enforceclientaffinity,andalsorequestsneedtoberetriedthroughthelistifservershavefailed,

sincefailureinformationisnotmaintained.

Edge Transport Server Role Availability

HighAvailabilityfortheEdgeTransportServerrolecanbeprovidedbydeployingmultipleEdge

serversintheperimeternetworkandloadbalancingrequestsusingDNSRoundRobindescribed

in the earlier section or using multiple mail exchangers (MX) records in the DNS. DNS

documentation of the implementation deployed can provide further configuration details on

thesemethods.

Multiple

Edge

Transport

servers

can

be

deployed

using

these

methods,

dependingontheloadbalancingneeds.

Unified Messaging Server Role Availability

HighAvailability for theUnifiedMessaging server role canbeprovidedbydeploying twoor

moreUnifiedMessaging(UM)servers.IfVOIPgatewaydevicesaredeployedbetweentheUM


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serversand thePrivateBranchExchange (PBX), then twoormore identicallyconfiguredVOIP

gateways may be deployed to ensure their high availability. The UM servers need to be

configuredaspartofthesamedialplan.TheVOIPgatewayscanbeconfiguredtoloadbalance

callsacrosstheseserversusingRoundRobinmethodsandalsoreroutecallstoanotherserverif

oneoftheservers isdown.DeploymentswhereanIPbasedPBXisdirectlyconfiguredtoroute

callstoUMserversshouldbeconfiguredforthesameloadbalancingandreroutingfunctionality.

MultipleUMserversandVOIPgatewayscanbedeployedbasedonavailabilityandscalability

needs.


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High Ava i lab i l i ty Deployment

Cons iderat ions

TheLCR,CCR, and SCC features cannotbedeployed to coexist on the samemailbox serverconfigurationandaremutuallyexclusive.AmailboxservercanbeconfiguredwithLCR,CCR,or

SCC. If theMailboxserver role isdeployed inahighlyavailableclusteredconfigurationusing

SCC or CCR based on Microsoft Cluster Services (MSCS), no other server role can be

consolidatedwith theMailbox role on the same server. Thus for SCC orCCR deployments,

separate servers need tobeprovisioned fordeploying theHubTransport,ClientAccess, and

other roles.Consolidating server roles onmultiple servers requires careful consideration.An

examplescenariomaybeconsolidatingHubTransportandClientAccessroleson twoservers,

withboth roles consolidatedonboth servers forHA.Since eachof the server roles requires a

differentmethodforachievingHA,carefulplanningisrequiredtoensuretheirinteroperability.

Regardlessof

specific

consolidation

and

deployment

scenarios,

hardware

for

each

server

role

shouldbeplannedandsizedappropriatelyforbothcapacityandperformance.


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Conclus ion

ExchangeServer2007providesnewavailabilityoptionsthatenablebusinessestoeffectivelymeet

their

availability

requirements

and

protect

their

messaging

systems

against

hardware

failures.

Administratorsshouldcarefullyevaluatethelevelandtypeofavailabilityrequiredbefore

decidingwhichoptionismostappropriatefortheirenvironment.Thechoiceofaparticular

optionwilldependonvariousfactorssuchascost,downtime,recoverability,scalability,and

manageability. Implementingtherequiredavailabilityfeaturesandconfiguringthemforoptimal

performancecanhelpcreateflexible,highlyavailablesystemsinenterprisedatacenters.

DellPowerEdgeservers,DellPowerVaultstorage,andDell|EMCstorageprovidestandard

hardwareplatformsforseamlesslydeployingExchangeServer2007withtherequiredavailability

features.Moreinformationcanbeobtainedatwww.dell.com/exchange.DellServicesinclude

assessment,design,andimplementationtailoredforthosemessagingdeployments.Dellalso

offersendtoendExchangemessagingsolutionsthatincludepartnerofferingsforsecurity,

archiving,backup,

and

recovery.

More

information

can

be

obtained

at

www.dell.com/secureexchange.

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Dell Ha Exchange 2007