VDI and snapshots: A winning combination

Transcription

1 ANALYSTVIEW VDIandsnapshots:Awinningcombination ByRayLucchesi January2009InfoStor Theproliferationofuserdesktopsisrapidlybecominganadministrativequagmire fortoday'sdatacenters.however,desktopvirtualizationproductshaverecently emergedtoreducethenegativeeconomicimpactofdeployingamultitudeof desktops. VMwareVirtualDesktopInfrastructure(VDI)isonesuchpackage,andprovides desktopvirtualizationbyusingvirtualmachinestoexecutesoftwarewhileonly runningaremotedesktopclientontheuser'sdesktop.consequently,vdiprovides easydesktopconsolidationandreducestheoverallcostofdeployingenterprise desktopservices. ButVDIimplementationhasatleastoneprominent,yetresolvable,concern. Specifically,VDIrequirescopiesofbootimagedataonexpensive,centralized storageforeachvirtualdesktop.snapshotserviceshelpresolvethisconcernby moreefficientlyreplicatingthebootimagedata,andthussignificantlyshrinkingthe incrementalstoragecostspervirtualdesktop. Ontheotherhand,notallVDIdataissuitableforsnapshots.Forinstance,virtual desktopsalsorequirestorageforuserworkspace.becauseuserworkspacedatais uniquetoeachdesktop,itmakeslittlesensetoreplicateviasnapshots.moreover, thisdatacouldeasilybecentralizedandco locatedonsharedvmfsdatastores. Snapshotsforbootimages Normally,tocreatemultiplebootimages,bootimagedatamustbecopied.Oneboot imagetypicallytakes10gbto20gbofspaceandwouldtakeonlyashorttimeto copy.however,making100copiesof20gbbootimageswouldtakemorethanfive hoursat100mbps(possiblydoublethatifthesourceandtargetareonthesame storage)andtake2tbofspace. Amoreeffectiveapproachistousesnapshottechnologytocreatethemultipleboot imagecopies.snapshotsprovideforinstantaneous,space efficientreplicationof dataonmoststoragesubsystems. 2009InfoStor Page1of5 AllRightsReserved

2 ANALYSTVIEW TherearethreedifferentapproachesforsnapshotsthatcanbeusedtosupportVDI bootimages: Snapshotsofrawdevicemode(RDM)physicalmodeLUNs VMware supportsrdm,whereavirtualmachinebootsdirectlyfromaphysicallun, bypassingvmwarei/ovirtualization.anadministratorwouldtypically createthebootimageonasinglelun,andthenthisluncouldbesnapshot asmanytimesasneeded. Snapshotofasinglebootimagedatastore Thevirtualdesktopbootsfrom a".vmdk"filethatisthesolediskimagefileonadatastoreresidingona singlelun.anadministratorwouldcreateavmfsdatastore,createagold bootimageonthedatastore,andthenrepeatedlysnapshotthelunholding thedatastoretocreatetherequisitenumberofbootimagecopies. Snapshotofamultiplebootimagedatastore Inthisapproach,multiple bootimagesresideonthedatastoreandcanbereplicatedviasnapshots simultaneously.aswiththesnapshotofasinglebootimage,the administratorcreatesavmfsdatastoreonasinglelunandthencreatesthe Goldbootimage.Atthispoint,theGoldbootimagewouldbecopiedtocreate themultiplebootimagesonthedatastore.themultiplebootimagedatastore would,asafinalstep,besnapshotasmanytimesasneeded.forexample,to createadatastoreof10bootimages,thegoldbootimagewouldbecopied ninetimes,resultingin10copiesofthebootimageforeachsnapshot. Snapshotconcerns SnapshotsofVDIbootimagesareconstrainedbyLUNorfilesystemgranularityand thusareamajorconcern.vdibootimagedataistypicallyjustoneofmany".vmdk" filesonasharedvmfsdatastore,configuredoveranumberofluns.snapshotting thisdatastorewouldreplicateallthe".vmdk"filesalongwithbootimagedata,and unnecessarilyconsumeluns,wastingvaluableresources.assuch,vdibootimages shouldbeisolatedinasinglelundatastoreforsnapshotpurposestomaximizevdi utilityandminimizestorageconsumption. AconcernarisingfromthisLUNproliferationcausedbysnapshotsistherecognized axiomthatmorelunsnecessarilymeansmorework;i.e.,morestorage configuration,morebackupchanges,andmorespacemanagementmonitoring. However,bootimagesnapshotdataisbasicallynon growingdata,andassuch shouldnotaddtospacemanagementproblems.furthermore,bootimagebackup changesareonlydoneonce,andbootimagedatadoesnotneedfrequentbackup becausechangesarerare.finally,theconfigurationchangesneededtodefine additionallunscanbemitigatedbecausethesearesubsystem createdlunsin responsetosnapshotcommands.giventhesefactors,addingbootimagesnapshot LUNsshouldrequiresubstantiallylessincrementalmaintenancethanother,nonstaticLUNs. 2009InfoStor, Page2of5 Allrightsreserved

3 ANALYSTVIEW Forlargerdatacenterssupportingnumerousdesktops,thepotentialforLUN proliferationcouldbecritical.usingsnapshotsofmultiplebootimagedatastores couldmitigatethislunproliferationconcern.forinstance,vmwarevirtual Infrastructure3(VI3)onlysupportsamaximumof256LUNsperESXserver.Not alloftheselunscanbevdibootimages,assomemustbeusedforend user workspaces,non desktopvirtualmachinestorage,andvi3software.withfourboot imagesperdatastore,125snapshotswouldsupport500virtualdesktopsandstill leavemorethan130esxlunsforotherstoragerequirements. Multiplebootimagesperdatastoremaynotalwaysbeadvantageous,however.In fact,whenrestoringasingledesktopimage,suchanapproachmaybeslower.in thiscase,insteadofaquicktwo step"point and shoot"mountandbootofanew snapshot,itbecomesaslowerthree stepprocessofmountingtheappropriategold imageorbackupvolume,copyingthecorrectbootimagetotheluninuse (potentiallyaslowprocess),andrestartingtheclient. AsecondissuewiththemultiplebootimageperdatastoreapproachisLUN level monitoring.here,thegranularityofstoragemonitoringonlyallowsviewingactivity atalunleve,landassuchcannotmonitortheactivityofasingledesktopbut insteadviewstheaggregationofallthedesktopsassignedtothelun. Mostvendorsuse"copy on write"technologytoprovidestoragesubsystem snapshots.thistechnologycopiesdataonlyasit'smodifiedandthusisidealfor rarelychangedbootimagedata.however,vendorsvarywidelyintheirsupportof snapshotservices.specifically, NotallstoragesubsystemssupportlargenumbersofsnapshotsperLUN.For example,hdsusp Vlimitsthenumberofcopy on writesnapshotstoone perlun;ibmds8000limitsthenumberofflashcopysesnapshotsto12per LUN,andEMCSymmetrixlimitsthenumberofTimefindersnapshotsto16 perlun. Notallsnapshotsarewritable,andoftentherearelimitstothenumberof writablesnapshotsfromthesamelun.forexample,3parallows128 writableand500read onlysnapshotsperlun.netapphasbothread only snapshotsandwriteableflexclonevolumes,butactuallimitsarenotreadily specified. Notallstoragesnapshotsreservethesameamountofdiskspace.Some subsystemscanreserveupto40%ormoreoftheoriginallunforsnapshot space,althoughafewvendorsreservenoadditionalspacefortheir snapshots Notallstorageproductssupportspace efficientsnapshots.forexample,when asourcelunismodified,anewspace consumingblockwouldpotentially needtobecreatedforeachlunsnapshot.somesystems,however,provide anon duplicativefeature,soonlyonecopyoftheupdateoccursregardlessof thenumberofwriteablesnapshots,resultinginlessstorageconsumption. 2009InfoStor, Page3of5 Allrightsreserved

4 ANALYSTVIEW Firstandforemost,usingsnapshotsforbootimagedata speedsupend userdesktopdeployment. Snapshotbenefits Firstandforemost,usingsnapshotsforbootimagedataspeedsupend userdesktop deployment.copyingtbsofdatanormallytakeshours,butwhenusingsnapshots,it takesjustminutes.anothersnapshotadvantageisdesktopbootperformance. Finally,usingsnapshotsresultsinconsiderablestoragespacesavings.Forexample, assuminga20gbbootimage,2tbofstoragewouldbenecessarytosupport100 desktops.using99snapshotsofthesamebootimage,andthusstillsupporting100 desktops,mayonlytake20gbofstorage a99%reduction. GiventhecompellingbenefitsandresolvableconcernsofsnapshotsforVDIboot images,administratorsusingvdibootimagesnapshotsstillhaveadifficulttask. Oncetheyhavecreatedabootimage".vmdk"file,theyneedtolocatetheVMFS datastoreitresideson,determinethelunholdingthedatastore,locatethephysical storagethislunresideson,issuetherequisitesubsystem specificrequeststo snapshotthedatastore,andthenexportthenewlunstoesx.followingtheexport, theadministratormustsignalvmwaretore scanfornewlysnappedluns,andto re signaturethesnapshotvolumesforvdivirtualmachinesuse.finally,the administratormustclonethevirtualdesktopconfigurationandattachthevirtual machinetousethenewlycreatedbootimage. Recognizingthetediousnessofmanyoftheseconfigurationtasks,somevendors providescriptstoautomatemuchoftheprocess.forexample,3par'sthincopy DesktopforVMwareVDIscript,suppliedasacustomizablescript,usestheVMware "perlapi"tomapthebootimagefromavmfsdatastoretoalun,directsthe subsystemtosnapshotthesourcelunmultipletimes,exportsthenewlunstoesx, andsignalsvmwaretore scanandre signaturetheresultantlun(s),whichare madevisiblewithinthevcenterinventory.whilenotallconfigurationtaskshave beenscripted,muchofthedrudgeryoftraditionalstorageprovisioninghasbeen eliminated. VMwareVDIisaprovenandsuccessfulproductfordeployingmultipledesktopsin anenterprise,andsnapshotsofvdibootimagedatacansignificantlyenhancevdi. 2009InfoStor, Page4of5 Allrightsreserved

5 ANALYSTVIEW Infact,thecaseforbootimagesnapshotsiscompellinginavastmajorityof situations.toreiteratethebenefits: Lengthycopyingprocessescanbeperformedinminutesratherthanhoursor days Boottimesformultipledesktopscanbesignificantlyreduced Substantialstoragespacesavingsofbootimagedatacanberealized often75% ormore. Examinationoftheimplementationdifferencesbetweensubsystemsiscritical becausevendorsdonotsupportsnapshotsinthesameway.decision making factorsshouldincludeautomateddesktopprovisioning,space efficientsnapshots, efficientsnapshotcaching,andhighavailability. InfoStor January 2009 About the author Ray Lucchesi is president of Silverton Consulting, a Storage, Strategy & Systems consulting services company, based in the USA offering products and services to the data storage community. mailto:[email protected] InfoStor, Page5of5 Allrightsreserved