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DELLDellTM | Cit rix XenServerDell Edit ionReference Architec ture
VIRTUALIZATION SOLUTIONS ENGINEERINGSeptember 2008
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THISWHITEPAPER ISFOR INFORMATIONALPURPOSESONLY,ANDMAYCONTAINTYPOGRAPHICALERRORSAND
TECHNICAL INACCURACIES.THECONTENT ISPROVIDEDAS IS,WITHOUTEXPRESSOR IMPLIEDWARRANTIESOF
ANYKIND.
Dell, the DELL logo, EqualLogic, OpenManage, PowerVault, and PowerEdge are trademarks of Dell Inc.; Xen,XenServer,XenCenterandXenMotionareeitherregisteredtrademarksortrademarksofCitrixInc.;IntelandXeon
area registeredtrademarksof IntelCorporation in theU.S.andothercountries;AMD isaregisteredtrademark
andOpteron isatrademarkofAdvancedMicroDevices Inc.;Microsoft,Windows,Windows Vista,andWindowsServerareeithertrademarksorregisteredtrademarksofMicrosoftCorporationintheUnitedStatesand/orothercountries.
Othertrademarksandtradenamesmaybeusedinthisdocumenttorefertoeithertheentitiesclaimingthemarks
andnamesortheirproducts.Delldisclaimsproprietaryinterestinthemarksandnamesofothers.
Copyright2008DellInc.Allrightsreserved.Reproductioninanymannerwhatsoeverwithouttheexpresswritten
permissionofDellInc.isstrictlyforbidden.Formoreinformation,contactDell.
Informationinthisdocumentissubjecttochangewithoutnotice.
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Table of Contents
EXECUTIVESUMMARY.................................................................................................................................. 5
INTRODUCTIONANDSCOPE......................................................................................................................... 5
XenServerDellEditionIntroduction............................................................................................................. 6
CitrixXenServerDellEditionFeatures...................................................................................................... 6
FactoryinstalledfromDell.................................................................................................................... 6
Integratedsystemsmanagementandmonitoring............................................................................... 6
XenServerLocalConsole....................................................................................................................... 6
Optimizedfootprintandcontrolledenvironment................................................................................ 6
Improvedreliability............................................................................................................................... 6
ImprovedXenServerupdates............................................................................................................... 6
Precertifiedandsupportedconfigurations......................................................................................... 6
Dell|CitrixXenServerReferenceArchitecture............................................................................................ 7
SmallConfiguration................................................................................................................................... 9
MediumConfiguration............................................................................................................................ 10
HardwareConsiderationsforXenServerEnvironments............................................................................. 11
References.................................................................................................................................................. 13
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EXECUTIVESUMMARYThisDellVirtualizationReferenceArchitecture(RA)whitepaperdescribesvalidatedarchitecturesfor
Dell|CitrixXenServerDellEditionvirtualinfrastructures.TheVirtualizationRAisintendedtoprovide
customerswithanexamplebasistoconsider,evaluate,andselecttheDellvirtualizationsolution
componentsthatbestfittheirrequirements. Thisdocumentisnotintendedtobeanexhaustivestudy
ofspecificarchitecturesforeveryenvironment. Foracompleteevaluationofyourdatacenters
virtualizationrequirements,pleasecontactyourDellSalesrepresentative.
INTRODUCTIONANDSCOPECustomersarefacedwithmanychoiceswhenplanningavirtualizationdeployment.Server,storage,and
softwareconfigurationscanvarydependingonworkloadandfeaturerequirements.Thispaperproposes
severalsamplevirtualizationarchitecturesbasedonDellsserverandstorageproducts. Architectures
aredivided intothreemaincategories:Small,Medium,andLarge. Thesecategoriesarebasedonthe
featuresandcapacityofeachproduct,aswellasthecomplexityoftheoverallarchitecture. TheSmall
architecture is designed with simplicity in mind and focuses on providing basic functionality with
minimalhardware. Itdoesnotenableadvancedvirtualizationfeatures.TheMediumconfiguration is
designed to meet the production requirements of small and medium businesses by providing
economical SAN solutions, enhanced virtualization features, and backup options. Finally, the Large
configuration is a fullfeature virtualization solution using redundancy,1tomanymanagement, high
availabilityandenterpriseclassserverandstorageproducts.Thegoalsofthedocumentareasfollows:
IntroducecustomerstotheDell|CitrixXenServersamplereferencearchitectures. Clarify,aid,andsimplifythedecisionmakingprocessforcustomers.
ThescopeofthisdocumentislimitedtoDell|CitrixXenServerDellEditionvirtualizationsolutionsonly.
ItdefinesarchitecturesusingDellservers,storage,andnetworkingcomponents.Smallerarchitectures
using free products are possible, but are not described here. Custom configurations for specific
customerengagementsmayhavethirdpartyhardwareorsoftwareandhenceareoutofscope.
Thisdocumentisastartingpointinthedesignofavirtualizationsolution. Dellprovidesseveral
resourcesforthecompletedesignanddeploymentofvirtualizationsolutions. Forfurtherinformation
pleasevisitwww.dell.com/citrixorwww.dell.com/virtualizationforthelatestupdatedversions.
Thedocumentisarrangedasfollows:Section2includestheintroductionanddetailsthescopeofthe
document;Section3describesDell|CitrixXenServerDellEditionfeature,Section4describestwo
referenceconfigurations,Section4describesgeneralsizingconsiderationsandSection5containsthe
referencelinks.
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XenServerDellEditionIntroductionWith the64bitopensourceXenhypervisorat its core,CitrixXenServerDellEdition isapowerful
virtualization solution that enables efficient resource consolidation, utilization,dynamic provisioning,
andintegratedsystemsmanagement.XenServerDellEditionhasasmallfootprintand isoptimizedto
runfroman internalflashstorage inDellPowerEdgeservers.DellandCitrixhavepartneredtobring
prequalifiedandvirtualizationreadyplatformsfortoday'sdynamicandgrowingdatacenters.
CitrixXenServerDellEditionFeatures
FactoryinstalledfromDell
CitrixXenServerDellEditionisfactoryinstalledfromDellonselectPowerEdgeservers.Thisreducesthe
installationanddeploymenttimerequiredandsimplifiesthedeploymentprocesstogetyour
infrastructurereadytouse.Withminimalconfiguration,theXenServerhostisavailabletorunvirtual
machines.
Integratedsystemsmanagementandmonitoring
CitrixXenServerDellEditioncomespreinstalledwithDellOpenManageServerAdministrator.This
enablessystemsmanagementrightoutoftheboxwithoutanyadditionalneedtoinstallanagentonthe
host.
XenServerLocalConsole
TheXenServerDellEditionincludesanewXenServerLocalConsoleuserinterfacetoenablelocaladministrationof
thehost.XenServerLocalConsoleenablesuserstoconfigureandviewhostspecificpropertiessuchas
managementnetworkconfiguration,localstorageforvirtualmachines,etc.XenCenter,thestandardMicrosoft
WindowsmanagementconsolefortheXenServer,isalsoavailable.
Optimizedfootprintandcontrolledenvironment
XenServerDellEditionisoptimizedforasmallerdiskfootprintandwritestoflashstorage.Themajorityofthe
XenServerDelleditionfilesystemisReadOnlyandthusprovidesatightercontrolovertheXenServeroperating
environment.TheXenServerDellEditionhostagentsoftwarehasbeensignificantlyoptimizedtominimizethe
numberofwritecyclestotheflashstorage.XenServerwritestoflashstorageonlywhensomethingimportanthas
changedandmustberecorded.Writeminimizationhelpsimprovethelifeoftheflashstorage.
Improvedreliability
RunningXenServerDellEditiononaserver'sinternalflashstorageprovidesimprovedreliabilityoverrunningon
traditionalharddisks.Flashstoragedoesnothavemovingpartsandismorereliablethanaharddisk.
ImprovedXenServerupdates
Toimprovereliabilityofsoftwareupgrades,theXenServerDellEditionimagecontainsaprimaryandsecondary
copyoftheXenServerfilesystem.Anytimeanupdateisapplied,thesecondarycopygetsupdatedleavingthe
primarycopyinaknowngoodstate.Thesecondarycopybecomestheprimaryafterasuccessfulupgrade.An
updatetotheXenServerhostcanbeappliedusingtheXenServerlocalconsoleorXenCenter.
Pre certifiedandsupportedconfigurations
CitrixXenServerDellEditioniscertifiedandfullysupportedbyDellforselectserverandstorageconfigurations.
BothDellandCitrixhaveworkedcloselytoprovidethehighestqualityproductanduserexperience
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Dell|CitrixXenServerReferenceArchitectureTheDell|CitrixXenServerreferencearchitecturerepresentsapossiblesamplesolutionthatprovidesa
customerwithoptionstoconsiderwhenmeetingtheirdatacenterrequirements. InDellsreference
architecture,DellserverandstoragearethefoundationonwhichCitrixXenServerinfrastructureisbuilt.
SpecificXenServerfeaturesshouldbechosenbasedonthedatacenterneeds. Oncechosen,thesekey
XenServerfeatureswilldrivehardwarerequirements. Therefore,thefeaturesareasimportanttothe
designanddecisionprocessasthetraditionalQoSdeliverables.
Twosampleconfigurations:SmallandMediumarelistedhere.Theseconfigurationsaregeneric
deploymentsbasedonsolutionsizeandcapabilityandareindependentofthetargetapplication. The
recommendationsfocusonhardwarecapacityandsoftwarefeatures;theydonotattempttoprescribea
particularservermodelorchipset,asthesepreferencesmayvarybasedoncustomerrequirements.
Thefollowingtabledescribessamplecomponentsforeachconfiguration.CitrixXenServerfeaturesare
listedbelowandenabledwithrecommendedDellserverandstorage. Theseareexamplesofbaseline
architecturesthatcanbebundledtogetherintoadatacentertosolvecustomerproblems.
Table1:HardwareandSoftwarefeaturesoftheBaselineConfiguration
Small Medium
Description Simpleentrylevel
configuration
Designedforsmall&medium
business
ServerConfiguration
Servers PE2900III,
PE1950III
PER805
PEM600
PEM605
PEM805
PEM905
PE2950III
PER805
PER900
PER905
CPU 2Sockets/DualCore 2Sockets/QuadCore
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MinimumNICports Two(twoLANonMotherboard
ports)
Fourtosix(TwotofourLAN
onMotherboardportsplus
additionaladdinifnecessary)
DRAC Optional Yes
LocalStorage 5x73GB/
5x146GB
2x73GB
Internalstorage
controller
PERC6/iorSAS6/iR
(RAID1,5)
PERC6/iorSAS6/iR
(RAID1,5)
StorageConfiguration
StorageFabric LocalorexternalSAS/SATA
storage
NetworkbasediSCSI
StorageArray LocalStorage,MD1000,
MD1120
MD3000
MD3000i,
PS5000E,PS5000X,
PS5000XV
BackupServer N/A PE2900
BackupSoftware N/A BackupExec11D
BackupDevice N/A PowerVault
TL4000
SoftwareConfiguration
CitrixXenServerDellExpressor
EnterpriseEdition
CitrixXenServerDell
EnterpriseEdition
XenMotionlive
migration
Yes* Yes
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HighAvailability Yes* Yes
ResourceQoS
Controls
Yes* Yes
Multiserver
management
Yes* Yes
Resourcepools Yes* Yes
SharedIPbased
storage
Yes* Yes
VLANconfirmation Yes* Yes
DellEqualLogic
StorageAdapterYes Yes
Management
XenCenter Yes Yes
ITA Optional Yes
OpenManage
Administrator
Yes Yes
*FeatureisavailableonlyinCitrixXenServerDellEdition
SmallConfiguration
TheSmallconfigurationisdesignedtobeasimpleentrylevelconfiguration.EachserverisrunningCitrix
XenServerDellExpressorEnterpriseEdition. Thestoragerequirementsareexpectedtobelowsolocal
storagemaybesuitableforsomedeployments. Butdirectattachoptionsarealsoavailablewiththe
MD1000,MD1120,orMD3000.
Figure1belowisasampleinstanceofasmallconfigurationanddoesnotreflectallpossiblesmall
configurations. Itprovidesahighlevelviewofasmallconfiguration;butitalsohighlightsthatsomekey
XenServerfeaturesarenotconfigurablewithintheconstructofasmallconfiguration. Therefore,there
isaneedtoabstracthigherorderconfigurationssuchastheMediumandLargeconfigurations. Inthis
example,CitrixXenServerDellEditionisdeployedontwoPowerEdge2900IIIserversthatareattached
toaPowerVaultMD3000array.UsingMD3000array,thetwoXenServerhostscanshareastorageLUN,
thusenablinglivemigrationorXenMotionofvirtualmachineacrosstwohosts.PowerVaultMD3000
providesanidealenvironmentforsmallusewherehostscalabilityisnotabigconcern.PowerVault
MD3000providesupto15TBofrawdiskcapacityusing15SASorSATAdrives.UptotwoPowerVault
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MD1000diskenclosures,eachenclosureprovidingamaximumof15TBofrawstoragecanbedaisy
chainedtoPowerVaultMD3000toincreaserawstoragecapacitytoatotalof45TB.UsingSASHBAson
XenServerhostsanddualcontrollersonMD3000providesredundancyagainstanHBA,controllerorSAS
interconnectfailure.
AsabestpracticeitisrecommendedtosegregateXenServerhostmanagementtrafficfromother
managementtrafficsuchasstoragemanagement.NotethatinXenServer,themanagementnetwork
interfaceisusedforXenMotionorlivemigrationtraffic.Trafficsegregationcanbeachievedbyusing
separatephysicalswitchesorusingseparateVLANs.Asshowninthefigure,highavailabilityandload
balancingforvirtualmachinetrafficcanbeachievedbybondingtwoNICsoneachXenServerhost.
Figure1:AsamplesmallconfigurationforCitrixXenServerDellEdition
MediumConfiguration
TheMediumconfigurationistargetedtowardssmallandmediumbusinesscustomerstoenableboth
hostandstoragescalabilitythatismorethanwhatisofferedbythesmallconfiguration.Each
PowerEdgeserverrunningCitrixXenServerDellEnterpriseEditionenablescustomerstouseadvanced
featuressuchasresourcepools,integratedHA,XenMotion,andresourceQoS.
Figure2belowisasampleinstanceofamediumconfigurationanddoesnotreflectallpossiblemedium
configurations.CitrixXenServerDellEditionrunsonDellPowerEdgeR805servers,configuredina
resourcepool. AllXenServerhostsareconnectedviaanEthernetfabricandsharestorageontheDell
EqualLogicPS5000array(s). TwoNICsoneachhostareconfiguredasabondtoprovidehighavailability
foriSCSIstoragetraffic.TheiSCSItrafficisisolatedfromothernetworktrafficusingseparatephysical
Ethernetswitches.TwoNICsoneachhostarebondedtoprovidehighavailabilityandloadbalancingfor
virtualmachinetraffic.TwoNICsoneachhostarebondedtoprovidehighavailabilityandloadbalancing
forthehostmanagementandXenMotiontraffic.Thisconfigurationillustratestrafficsegregationusing
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separatephysicalswitches;howeverisolationcanalsobeachievedusingVLANs.XenCentercanbe
installedonanyworkstationorservermachinethathasaccesstothehostmanagementnetwork.
Figure2: AsamplemediumconfigurationforCitrixXenServerDellEdition
Upto16hostscanbeconfiguredaspartofasingleresourcepool.Beingpartofaresourcepoolallows
XenServerhoststoshareiSCSIstorageonPSSeriesarrays.Sharedstorageisarequirementforlive
migrationorXenMotionofvirtualmachine,providinguninterruptedVMmigrationfromonephysical
hosttoanother.UsingsharedstoragealsoallowsuserstoconfiguretheXenServerpoolforHigh
Availability,anewfeatureavailableinXenServer5.0.Dependingonthepoolconfigurationandrestart
priorityofVMs,incaseofahostfailure,XenServerHAfeaturerestartsvirtualmachinesonremaining
healthyhostsinthepool.
XenServer5.0alsointroducesadirectstorageadapterforDellEqualLogicPSSeriesarrays.Usingdirect
storageadapterforPSSeries,storagemanagementtasksforvirtualmachinescanbeachieveddirectly
usingXenCenterinterface.ThestorageadapteralsoenablesadvancedPSseriesfeaturessuchascloning
toinstantaneouslydeploynewvirtualmachines,virtualmachinessnapshots,thinprovisioning,etc.
HardwareConsiderationsforXenServerEnvironments
Thissectionprovidesgeneralscalingconsiderationsforhardwarewhendesigningavirtualized
infrastructure. Theguidancefocusesaroundthefourmajorhardwaresubsystems:(1)CPU;(2)memory;
(3)disk;and(4)network. Thesefoursubsystemsareimportanttounderstandinthegeneralsense
becausenotplanningforthemcanleadtopoorqualityofservice(QoS)inthedatacenter.
TheCPUsubsystemisakeycomponentindeliveringacceptableQoSinthedatacenter. Thedecision
hingesonchoosingtherightnumberofprocessorsandprocessortype.Inaddition,choosingbetween
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dualcoreprocessorsandquadcoreprocessorsinvolvemanyfactorssuchascostandperformance.
Ultimately,theserverneedsenoughphysicalCPUresourcestomeettheneedsofthevirtualized
infrastructureandtheneartermgrowth. Inshort,improvingCPUperformancecanbeaccomplishedby
choosingserverswithmoreprocessorcapacity,pickingprocessorswithhigherfrequencybinsor
upgradingtoquadcoreprocessorsfromdualcoreprocessors.
WhensizingCPUrequirementsforXenServer,itisfairtoassumethatoneprocessorcorewillbeusedby
theXenServerplatformwhiletheremainingavailableforusebythevirtualmachines.Thecontrol
domainisallocatedoneCPUandhenceusesoneoftheavailablecoresinthehost.XenServerDell
Editionsupportsupto8virtualCPUsperVM,howevertheguestOSmaysupportadifferentnumber.It
isrecommendedtoconfigureavirtualmachineisonevirtualCPUandaddmorevirtualCPUsif
necessary.
ThememorysubsystemisanotherimportantcomponentindeliveringQoSinthedatacenter. Themain
decisionistochoosetherightamountofmemorytomeettheneedsofthedatacenterandbalanceit
againstthecostofmemoryandthecostofaddingadditionalsystems. Next,thememoryneedisdriven
bythenumberofvirtualmachines,theamountofmemoryneededbyeachvirtualmachine,theamount
ofmemoryneededbythehypervisortomanagethoseVMs,andthememorycushionformigration
considerations. Sincememorytendstobethefirstresourcetobecompletelyutilized,carefulplanning
willensureenoughcapacitytosustainandgrowthedatacenter.
InXenServer,outofthetotalphysicalmemoryavailableonthehost,aVMisallocatedthefullchunkof
configuredmemory.HencewhenplannedmemoryrequirementsforXenServerhost,aggregatememory
requirementsforallVMsshouldbetakenintoconsideration.MemoryconsumedbyXenServerplatform
(Xenhypervisorandcontroldomain)varieswiththetotalphysicalmemoryavailableintheserver.The
Xenhypervisoruses128MBofmemoryregardlessofthephysicalmemoryontheserver.Thememory
usedbythecontroldomainisalwaysatleast200MB,andisnevermorethan752MB;withinthatrange
itisscaledasalinearfunctionoftotalhostRAM.Forhostswithupto3.5GBofphysicalRAM,thecontrol
domainusageremainsat200MB;ona5GBhostthecontroldomainwilluse228MB;ona16GBhostthe
controldomainconsumes454MB;andonhostswith32GBormorethecontroldomainconsumes
752MB.Therefore,thetotalmemoryusedbyXenServerplatformrangesanywherebetween328MBto
880MB.
ThedisksubsystemneedstoprovideenoughstoragecapacitywhiledeliveringQoStothedatacenter
throughacceptableIOrequestresponsetimes. Inaddition,thenumberofhostsconnectingtothedisk
subsystemandthefabrictypeneedtobefactoredinordertopickthecorrectDellstorageenclosure.
ThecapacityportionisasimplecalculationbasedonRAIDlevelchoiceandcapacityneedsforvirtual
machinesandapplications. Theseconddesigncriteriainvolveperformancesizingthedisksubsystem
andprovidingenoughdiskspindlesandbandwidthtohandletheIOneed.Toprovidebetterserviceto
I/Ohungryvirtualmachines,XenServerDellEnterpriseEditionallowsonetospecifyvirtualdiskI/O
priorityforvirtualdiskonLVMbasedstoragerepositories.
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ThenetworksubsystemneedstodeliverQoSonIOrequests,connectthedatacenter,andenablekey
hypervisorfeatures. ThedecisionpointsinvolvechoosingenoughNICportstohandletheVMdata
traffic,managementtraffic,andstoragetraffic(ifany)andbuildingasolidfabricinfrastructuretomeet
currentneedsandallowforscalabilityasthedatacentergrows.
XenServerDellEditionsupportsupto6activephysicalnetworkinterfaces(orupto6pairsofbonded
networkinterfaces)perXenServerhostandupto7virtualnetworkinterfacesperVM.XenServer5.0
introducesactive/activeNICbondingthatenablesloadbalancingandfailoverforvirtualmachinetraffic
andfailoverforothertypesofnetworktraffic.ForfinergraincontrolovernetworkbandwidthQualityof
Service,I/Oprioritycanbeset(XenServerDellEnterpriseEditiononly)foravirtualmachinesnetwork
interfacetolimitthetransferratetodesiredkilobytespersecond. ForIPstorage,asabestpracticeitis
recommendedtouseahighlyavailablenetworkinfrastructure:hostNICportsconfiguredasabond,
redundantswitchesandstoragearraywithredundantnetworkports/controllers.Adedicatedprivate
networkforIPstorageisrecommendedtoisolatestoragetrafficfromvirtualmachineandhost
managementtraffic.
References
CitrixXenServerDellEditionSolutionGuide:http://support.dell.com/support/edocs/software/Citrix/
Dell|CitrixSolutions:www.dell.com/citrix DellVirtualizationSolutions:www.dell.com/virtualization XenServerDellEditionProductDownloads:www.citrix.com/xenserver/dell DellPowerVaultStorage:www.dell.com/powervault DellEqualLogicStorage:www.dell.com/psseries
Trademarksusedinthistext:Dell,theDELLlogo,EqualLogic,OpenManage,PowerVault,andPowerEdgearetrademarksofDellInc.;Xen,XenServer,XenCenterandXenMotionareeitherregisteredtrademarksortrademarksofCitrixInc.;IntelandXeonare
aregisteredtrademarksofIntelCorporation intheU.S.andothercountries;AMD isaregisteredtrademarkandOpteron isa
trademarkofAdvancedMicroDevicesInc.;Microsoft,Windows,WindowsVista,andWindowsServerareeithertrademarksorregisteredtrademarksofMicrosoftCorporationintheUnitedStatesand/orothercountries.Othertrademarksandtradenamesmaybeusedinthisdocumenttorefertoeithertheentitiesclaimingthemarksandnames
ortheirproducts.DellInc.disclaimsanyproprietaryinterestintrademarksandtradenamesotherthanitsown.