Download - 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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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
WindowsServer2003R2Enterprisex64EditionwithSP2;ExchangeServer2007
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
WindowsServer2003R2Enterprisex64EditionwithSP2;ExchangeServer2007
EnterpriseEditionHubTransport/ClientAccessserver Dell
PowerEdge
2900
with
2xQuad
Core
Intel
Xeon
X5355
2.66
GHz
processors;
16
GB
systemRAM
WindowsServer2003R2Enterprisex64EditionwithSP2;ExchangeServer2007
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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