IBMV系統(tǒng)存儲(chǔ)hyperswap實(shí)施手冊(cè)英文

IBMV系統(tǒng)存儲(chǔ)hyperswap實(shí)行手冊(cè)

文檔信息(文檔編號(hào)IBMSVC-70)文擋名稱作者電話QQIBMV系統(tǒng)存儲(chǔ)hyperswap實(shí)行手冊(cè)朱亞銘文檔修訂記錄編號(hào)修訂內(nèi)容簡述修訂日期修訂前版本號(hào)V1.0整體文檔旳編寫.12.23注：技術(shù)交流郵箱

一、ConfiguringanIBMHyperSwaptopologysystemAHyperSwap?topologysystemassistswithhighavailabilityandsitedisasterrecovery.AHyperSwaptopologysystemcanbeconfiguredthroughsiteallocationandtopologychangecommand-line(CLI)commands.ThemanagementGUIconfiguresaHyperSwaptopologywiththeModifySystemTopologywizard,whichguidesyouthroughallthestepseasily.1.1AboutthistaskToaccesstheModifySystemTopologywizard,selectMonitoring>System.IntheActionsmenu,selectModifySystemTopology.HYPERLINKConfiguringsiteinformationforthesystem

ToconfigureaHyperSwapsystemtopology,youmustassignenclosures,externalstoragesystems,andhoststoaspecificsite.HYPERLINKCreatingHyperSwapvolumes

YoucanusethemanagementGUIorthecommand-lineinterface(CLI)tocreateHyperSwapvolumes.AHyperSwapvolumehasonecopyoneachsite.HYPERLINKConvertinganexistingvolumetoaHyperSwapvolume

YoucanusethemanagementGUIorthecommand-lineinterfacetoconvertabasicvolumetoaHyperSwapvolume.Youconvertthebasicvolumebyaddinganothercopyofthevolumeinasecondsite.二、ConfiguringsiteinformationforthesystemToconfigureaHyperSwap?systemtopology,youmustassignenclosures,externalstoragesystems,andhoststoaspecificsite.2.1UsingthemanagementGUIYoucanusetheModifySystemTopologywizardinthemanagementGUItoeasilyconfigurethesitenamesandassignobjectsonyoursystemtoasite.TheModifyTopologywizardautomaticallydetectsanyFibreChannel-attachedstorage,butiSCSIstoragemustbeaddedmanuallybeforethesiteassignmentscanbeconfigured.YoucanuseeitherthemanagementGUIorthecommand-lineinterfacetoaddStorwizesystems.DellEqualLogficsystemscanbeconfiguredwiththecommand-lineinterfaceonly.CompletethefollowingstepstoconfigurethetopologyforthesystemandtooptionallyaddiSCSI-attachedstorage:InthemanagementGUI,selectMonitoring>System.IntheActionsmenu,selectModifySystemTopology.FollowthewizardtocompletetheconfigurationoftheHyperSwaptopology.IfyouareusingiSCSI-attachedexternalstorage,youmustaddthestoragetothesystemandspecifythesiteusingtheAddiSCSIExternalStoragewizard.Toaccessthewizard,selectPools>ExternalStorage>AddiSCSIExternalStorage.SelectIBMStorwizeastheexternalstoragesystemthatyouareadding.ThesystemsupportsiSCSIconnectionstoStorwizefamilyproductsandtoDellEquallogicsystems,butyoumustconfigureDellEqualLogicsystemswiththecommand-lineinterface.EntertheinformationforthesourceandtargetportsfortheiSCSIconnectionandspecifythesitefortheiSCSI-attachedstorage.2.2UsingtheCLIYoucanalsousethecommand-lineinterfacetoconfiguresiteinformationandconfigurethesystemasaHyperSwaptopology.Separatecommandsareusedforeachconfiguringsitedefinitionsforthenecessaryobjectsonthesystem.Althoughyoudonotneedtonamesites,creatingnamesthatarebasedonthelocationoruseofthesitesimplifiesmanagementoftheHyperSwaptopology.CompletethefollowingstepstoconfiguresiteinformationandsetthesystemasaHyperSwaptopology:ForeasiermanagementoftheHyperSwaptopology,createspecificnamesforeachsiteonthesystem.Ifnamesarenotspecified,sitescanbereferredtobytheirdefaultnameornumericID.Enterthefollowingcommandtocreatespecificnamesforeachsite.chsite-namelosangeles1Inthisexample,site1isnownamedlosangeles.TorenametheothersitesintheHyperSwaptopology,issuethesamecommandwithnamesfortheothersites:chsite-namesandiego2chsite-namequorum3Inthisexample,site2isnownamedsandiegoandsite3isnamedquorum.Note:IPquorumapplicationscanbeusedatathirdsitetoprovideatie-breakifthereisalossofconnectivitybetweensite1andsite2.Formoreinformation,seetheIPquorumconfigurationinformation.Enterthefollowingcommandstoassignexistingnodecanistersineachcontrolenclosure(I/Ogroup)tosites:chnodecanister-sitelosangelescanister1chnodecanister-sitelosangelescanister2Bothnodecanistersinacontrolenclosuremustbeassignedtothesamesite.Inthisexample,theI/Ogroupthatcontainscanister1andcanister2areassignedtothesitelosangeles.ToassignthenodecanistersinanotherI/Ogrouptotheothersite,enterthefollowingcommands:chnodecanister-sitesandiegocanister3chnodecanister-sitesandiegocanister4Inthisexample,theI/Ogroupthatcontainscanister3andcanister4areassignedtothesitesandiego.Youmustassignasiteforallnodecanistersinthesystem.Enterthefollowingcommandtoassignexistingexternalstoragesystemstosites:chcontroller–sitelosangelesstoragesystem1Inthisexample,storagesystem1isassignedtositelosangeles.Toassignastoragesystemtotheothersite,enterthefollowingcommand:chcontroller–sitesandiegostoragesystem2Inthisexample,storagesystem2isassignedtositesandiego.Ifyouplantouseanexternalstoragesystemtoprovidequorum,thenyoumustassignthattothethirdsite.Alternatively,anIPquorumapplicationcanbeusedtoprovidequorum.Formoreinformation,seetheIPquorumconfigurationinformation.Toassignanexternalstoragesystemtothethirdsite,enterthefollowingcommand:chcontroller–sitequorumstoragesystem3Inthisexample,storagesystem3isassignedtositequorum.Youmustassignasiteforallstoragesystemsthatarepresentintheconfiguration.Enterthefollowingcommandtoassignexistinghoststosites:chhost-sitelosangeleshost1Inthisexample,host1isassignedtositelosangeles.Ifyouhaveotherhosts,youcanassignthemtoothersites:chhost-sitesandiegohost2Inthisexample,host2isassignedtositesandiego.Afterallthesiteassignmentsarecompleteforenclosures,storagesystems,andhosts,setthesystemtopologytoHyperSwapbyenteringthefollowingcommand:chsystem-topologyhyperswapOptionally,configurebandwidthsettingsforthebackgroundcopyoperationsbetweeneachsitebyenteringthefollowingcommand:chpartnership-linkbandwidthmbits2048-backgroundcopyrate50mysystemBackgroundcopyisthetermthatisusedfortheinitialsynchronizationandanysubsequentresynchronizationtrafficforHyperSwapvolumesinthesystem.Afteryoucompletethesesteps,youcanconfigureHyperSwapvolumestocreatecopiesateachsite.2.3ConfiguringanexternaliSCSIcontrollerusingtheCLIAfteryouchangethesystemtopologytohyperswapandnodesareassignedsites,youcanconfigureanexternaliSCSIcontrollerbycompletingthefollowingsteps.Fromthenodesofsite1,discovertheiSCSItargetcontroller:detectiscsistorageportcandidate–srcportid1-targetipIP1-site1Checkthestatusofthediscoveredtargets:lsiscsistorageportcandidateidsrc_port_idtarget_ipv4|target_ipv6target_iscsinameiogroup_listconfiguredstatussite_idsite_name01IP1IQN11:1:1:1noFull1site1Fromthenodesofsite1,addasessiontothediscoveredtargets:addiscsitorageport-site10Fromthenodesofsite1,viewtheestablishedsessionswiththetarget:idsrc_port_idtarget_ipv4|target_ipv6target_iscsinamecontroller_idiogroup_liststatussite_idsite_name03IP1IQN151:1:1:1full1site1Thenewcontrollercanbeshownasavailablebyenteringthelscontrollercommand.Assignasite:chcontroller-site1controllerIDFromthesystemnodesofsite2,repeatsteps1through5fordiscoveringandestablishingsessionstothesameiSCSIcontrolleroradifferentiSCSIcontroller.三、CreatingHyperSwapvolumesYoucanusethemanagementGUIorthecommand-lineinterface(CLI)tocreateHyperSwap?volumes.AHyperSwapvolumehasonecopyoneachsite.3.1BeforeyoubeginBeforeyoucreateHyperSwapvolumes,youmustconfiguretheHyperSwaptopology.See\o"ToconfigureaHyperSwapsystemtopology,youmustassignenclosures,externalstoragesystems,andhoststoaspecificsite."Configuringsiteinformationforthesystemfordirections.3.2AboutthistaskAfteryouconfiguretheHyperSwaptopology,completeoneofthefollowingsteps.3.3ProcedureIfyouareusingthemanagementGUI,usetheCreateVolumeswizardtocreateHyperSwapvolumes.Ifyouareusingthecommand-lineinterface,usethemkvolumecommandtocreateavolume.Forexample,aHyperSwapvolumeiscreatedbyspecifyingtwostoragepoolsinindependentsites.mkvolume-size100-poolsite1pool:site2pool四、ConvertinganexistingvolumetoaHyperSwapvolumeYoucanusethemanagementGUIorthecommand-lineinterfacetoconvertabasicvolumetoaHyperSwap?volume.Youconvertthebasicvolumebyaddinganothercopyofthevolumeinasecondsite.4.1BeforeyoubeginBeforeyouaddacopyofthevolume,thesystemmustbeconfiguredwiththeHyperSwapsystemtopology.4.2AboutthistaskUsingthemanagementGUI:TochangeabasicvolumetoaHyperSwapvolumeinthemanagementGUI,selectVolumes,right-clickthebasicvolume,andselectAddVolumeCopies.Addacopyinadifferentsitetotheexistingcopy.Usingthecommand-lineinterface(CLI):IntheCLI,theaddvolumecopycommandaddsacopytoaHyperSwapvolume,whichchangesabasicvolumeintoaHyperSwapvolumewithcopiesontwoseparatesites.ToaddacopytoabasicvolumetoconvertittoaHyperSwapvolume,enterthefollowingcommand:addvolumecopy-poolsite2poolvolume5Inthisexample,site2poolisthestoragepoolontheothersite.AquorumdiskisanMDiskoramanageddrivethatcontainsareservedareathatisusedexclusivelyforsystemmanagement.Asystemusesaquorumdiskfortwopurposes:TobreakatiewhenaSANfaultoccurs,whenexactlyhalfofthenodesthatwerepreviouslyamemberofthesystemarepresent.Toholdacopyofimportantsystemconfigurationdata.Justover256MBisreservedforthispurposeoneachquorumdiskcandidate.HYPERLINKQuorumdiskconfiguration

Aclusteredsystemautomaticallyassignsquorumdiskcandidates.Whenyouaddnewstoragetoasystemorremoveexistingstorage,however,itisagoodpracticetoreviewthequorumdiskassignments.HYPERLINKIPquorumconfiguration

InsomeHyperSwap?configurations,IPquorumapplicationscanbeusedatthethirdsiteasanalternativetothird-sitequorumdisks.HYPERLINKManualquorumdiskoverrideinaHyperSwapsystem

Amanualquorumdiskoverrideisrequiredwhenyouexperiencearollingdisaster.Inraresituations,thesystemissubjecttowhatisreferredtoasarollingdisaster.Arollingdisasteroccurswhenanincidenthaswidescope,anditseffectsarefeltinmultiplestepsoveranextendedtimeperiod.Thefollowingexamplescenariodescribesarollingdisasterandshowshowtorecoverfromthatrollingdisaster.五、QuorumdiskconfigurationAclusteredsystemautomaticallyassignsquorumdiskcandidates.Whenyouaddnewstoragetoasystemorremoveexistingstorage,however,itisagoodpracticetoreviewthequorumdiskassignments.Itispossibleforasystemtosplitintotwogroupswhereeachgroupcontainshalftheoriginalnumberofnodesinthesystem.AquorumdiskdetermineswhichgroupofnodesstopsoperatingandprocessingI/Orequests.Inthistie-breaksituation,thefirstgroupofnodesthataccessesthequorumdiskismarkedastheownerofthequorumdiskandasaresultcontinuestooperateasthesystem,handlingallI/Orequests.Iftheothergroupofnodescannotaccessthequorumdiskorfindsthequorumdiskisownedbyanothergroupofnodes,itstopsoperatingasthesystemanddoesnothandleI/Orequests.Asystemcanhaveonlyoneactivequorumdiskthatisusedforatie-breaksituation.However,thesystemusesthreequorumdiskstorecordabackupofsystemconfigurationdatatobeusedintheeventofadisaster.Thesystemautomaticallyselectsoneactivequorumdiskfromthesethreedisks.Theactivequorumdiskcanbespecifiedbyusingthechquorumcommand-lineinterface(CLI)commandwiththeactiveparameter.Toviewthecurrentquorumdiskstatus,usethelsquorumcommand.Theotherquorumdiskcandidatesprovideredundancyiftheactivequorumdiskfailsbeforeasystemispartitioned.Toavoidthepossibilityoflosingallthequorumdiskcandidateswithasinglefailure,assignquorumdiskcandidatesonmultiplestoragesystems.Note:Mirroredvolumescanbetakenofflineifnoquorumdiskisavailable.Thesynchronizationstatusformirroredvolumesisrecordedonthequorumdisk.Important:Makesurethatyoumoveanyquorumdiskstoadifferentcontrollerbeforeyoudomaintenanceonaservicecontroller.InaStorwize?V5000systemwithasinglecontrolenclosureorwithoutanyexternalmanageddisks,quorumisautomaticallyassignedtodrives.Inthisscenario,manualconfigurationofthequorumdisksisnotrequired.InasystemwithtwoormoreI/Ogroups,thedrivesarephysicallyconnectedtoonlysomeofthenodecanisters.Insuchaconfiguration,drivescannotactastie-breakquorumdisks;however,theycanstillbeusedtobackupmetadata.IfsuitableexternalMDisksareavailable,theseMDisksareautomaticallyusedasquorumdisksthatdosupporttie-breaksituations.IfnosuitableexternalMDisksexist,theentiresystemmightbecomeunavailableifexactlyhalfthenodecanistersinthesystembecomeinaccessible(suchasduetohardwarefailureorbecomingdisconnectedfromthefabric).Insystemswithexactlytwocontrolenclosures,anuncontrolledshutdownofacontrolenclosuremightleadtotheentiresystembecomingunavailablebecausetwonodecanistersbecomeinaccessiblesimultaneously.Itisthereforevitalthatnodecanistersareshutdowninacontrolledwaywhenmaintenanceisrequired.Quorumconfigurationischosenbythefollowingcriteria:Thedriveisredundantandstable.Thedrivesareinacontrolenclosure.NounrecoverableerrorsareloggedagainstthedriveQuorumisdistributedamongtheavailablecontrolenclosures.Flashdrivesareavoided.Nearlineharddiskdrivesareavoided.Driveuseinorderofpriorityisspare,candidate,andthenmember.Thesecriteriaarenotrequirements.Onconfigurationswheremeetingallthecriteriaisnotpossible,quorumstillisautomaticallyconfigured.Itispossibletoassignquorumdiskstoalternativedrivesbyusingthechquorumcommand.However,youcannotmovequorumtoadrivethatcreatesalessoptimumconfiguration.Youcanoverridethedynamicquorumselectionbyusingtheoverrideyesoptionofthechquorumcommand.Thisoptionisnotadvised,however,unlessyouareworkingwithyoursupportcenter.Whenyouchangethemanageddisksthatareassignedasquorumcandidatedisks,followthesegeneralguidelines:Whenyouusequorumdrives,usedrivesfromthecontrolenclosurewhenpossibleforthebestavailableperformanceandconnectivity.IfnoexternalMDisksareavailable,atleastonedriveandideallythreedrivesinthecontrolenclosuremustbepresentandhaveausethatisnotunusedorfailed.WhenyouuseSAN-attachedquorumMDisks,aimtodistributethequorumcandidatediskssothateachMDiskisprovidedbyadifferentstoragesystem.Forinformationaboutwhichstoragesystemsaresupportedforquorumdiskuse,refertothesupportedhardwarelist.Beforeyouissuethechquorumcommand,ensurethestatusoftheMDiskordrivethatisbeingassignedasaquorumcandidatediskisreportedasonline.UsesmallercapacityMDisks,orusedrivesasthequorumdevices,tosignificantlyreducetheamountoftimethatmightbeneededtorunarecoversystemprocedure(alsoknownasTier3orT3recovery),ifnecessary.5.1QuorumMDisksordrivesinHyperSwapsystemconfigurationsToprovideprotectionagainstfailuresthataffectanentirelocation(forexample,apowerfailure),youcanuseactive-activerelationshipswithaconfigurationthatsplitsasingleclusteredsystembetweentwophysicallocations.Formoreinformation,seeHyperSwap?configurationdetails.FordetailedguidanceaboutHyperSwapsystemconfigurationforhigh-availabilitypurposes,contactyourIBM?regionaladvancedtechnicalspecialist.IfyouconfigureaHyperSwapsystem,thesystemautomaticallyselectsquorumdisksthatareplacedineachofthethreesites.Thefollowingscenariosdescribeexamplesthatresultinchangestotheactivequorumdisk:Scenario1:Site3iseitherpoweredofforconnectivitytothesiteisbroken.Iftopologyisstandard,thesystemselectsaquorumdiskcandidateatsite2tobecometheactivequorumdisk.IftopologyisHyperSwap,thesystemoperateswithoutanyactivequorumdisk.Site3iseitherpoweredonorconnectivitytothesiteisrestored.Assumingthatthesystemwascorrectlyconfiguredinitially,StorwizeV5000automaticallyrecoverstheconfigurationwhenthepowerisrestored.Scenario2:Thestoragesystemthatishostingthepreferredquorumdiskatsite3isremovedfromtheconfiguration.Ifpossible,thesystemautomaticallyconfiguresanewquorumdiskcandidate.InHyperSwaptopology,thesystemselectsonlyanewquorumdiskthatisinsite3.Inastandardtopology,thesystemselectsaquorumdiskcandidateatsite1or2tobecometheactivequorumdisk.Anewstoragesystemisaddedtosite3.Instandardtopology,theStorwizeV5000administratormustreassignallthreequorumdiskstoensurethattheactivequorumdiskisnowatsite3again.InHyperSwaptopology,thesystemautomaticallyassignsthenewactivequorumdiskwhenthestoragesystemisinstalledandthesitesettingisconfigured.5.2IPquorumconfigurationInsomeHyperSwap?configurations,IPquorumapplicationscanbeusedatthethirdsiteasanalternativetothird-sitequorumdisks.NoFibreChannelconnectivityatthethirdsiteisrequiredtouseanIPquorumapplicationasthequorumdevice.TheIPquorumapplicationisaJava?applicationthatrunsonahostatthethirdsite.TheIPnetworkisusedforcommunicationbetweentheIPquorumapplicationandnodecanistersinthesystem.Ifyoucurrentlyhaveathird-sitequorumdisk,youmustremovethethirdsitebeforeyouuseanIPquorumapplication.TherearestrictrequirementsontheIPnetworkandsomedisadvantageswithusingIPquorumapplications.Unlikequorumdisks,allIPquorumapplicationsmustbereconfiguredandredeployedtohostswhencertainaspectsofthesystemconfigurationchange.TheseaspectsincludeaddingorremovinganodecanisterfromthesystemorwhennodeserviceIPaddressesarechanged.OtherexamplesincludechangingthesystemcertificateorexperiencinganEthernetconnectivityissue.AnEthernetconnectivityissuepreventsanIPquorumapplicationfromaccessinganodethatisstillonline.IfanIPapplicationisoffline,theIPquorumapplicationmustbereconfiguredbecausethesystemconfigurationchanged.ToviewthestateofanIPquorumapplicationinthemanagementGUI,selectSettings>System>IPQuorum.YoucanalsousethelsquorumcommandtoviewthestateoftheIPquorumapplication.EvenwithIPquorumapplicationsatthethirdsite,quorumdisksatsiteoneandsitetwoarerequired,astheyareusedtostoremetadata.QuorumdisksforeachsiteareselectedautomaticallyandcanbeconfiguredinthemanagementGUI,byselectingPools>MDisksbyPools.YoucanalsousethechquorumcommandtoassignMDiskasaquorumdisk.AnIPquorumapplicationcanalsoactasthequorumdeviceforsystemsthatareconfiguredwithastandardtopologythatdonothaveanyexternalstorageconfigured.Thisconfigurationgivesasystemtie-breakcapability,automaticallyresumingI/Oprocessingifhalfofthesystem'snodecanistersareinaccessible.ThemaximumnumberofIPquorumapplicationsthatcanbedeployedisfive.Applicationscanbedeployedonmultiplehoststoprovideredundancy.5.3IPquorumrequirementsForstablequorumresolutions,anIPnetworkmustprovidethefollowingrequirements:ConnectivityfromtheserversthatarerunninganIPquorumapplicationtotheserviceIPaddressesofallnodecanisters.ThenetworkmustalsodealwithpossiblesecurityimplicationsofexposingtheserviceIPaddresses,asthisconnectivitycanalsobeusedtoaccesstheserviceassistantinterfaceiftheIPnetworksecurityisconfiguredincorrectly.Port1260isusedbyIPquorumapplicationstocommunicatefromthehoststoallnodecanisters.Themaximumround-tripdelaymustnotexceed80milliseconds(ms),whichmeans40mseachdirection.Aminimumbandwidthof2megabytespersecondisguaranteedfornodecanister-to-quorumtraffic.ThefollowingminimumrequirementsmustbemetonthehoststhatareusedtorunIPquorumapplications:Supportedoperatingsystems:RedHatEnterpriseLinux6.5,RedHatEnterpriseLinux7SUSELinuxEnterpriseServer11m3,SUSELinuxEnterpriseServer12SupportedJavaRuntimeEnvironments:IBM?Java7.1,IBMJava85.4InstallingIPquorumIfyouchangetheconfigurationbyaddinganenclosure,changingaserviceIPaddress,orchangingSSLcertificates,youmustdownloadandinstalltheIPquorumapplicationagain.TodownloadandinstalltheIPquorumapplication,completethefollowingsteps:InthemanagementGUI,selectSettings>System>IPQuorumandclickeitherDownloadIPv4ApplicationorDownloadIPv6ApplicationtocreatetheIPquorumJavaapplication.Youcanalsousethecommand-lineinterface(CLI)toenterthemkquorumappcommandtogenerateanIPquorumJavaapplication.Theapplicationisstoredinthedumpsdirectoryofthesystemwiththefilenameip_quorum.jar.TransfertheIPquorumapplicationfromthesystemtoadirectoryonthehostthatistoruntheIPquorumapplication.UsethepingcommandonthehosttoverifythatitcanestablishaconnectionwiththeserviceIPaddressofeachnodecanisterinthesystem.Onthehost,usethecommandjava-jarip_quorum.jartoinitializetheIPquorumapplication.ToverifythattheIPquorumapplicationisinstalledandactive,selectSettings>System>IPQuorum.ThesystemautomaticallyselectsMDisksforquorumdisks.InaHyperSwapconfigurationwithIPquorum,thesystemautomaticallyselectsanMDiskfrombothsites.TheseMDisksstoremetadatathatareusedforsystemrecovery.IfyouwanttoselectspecificMDisktouseasquorumdisks,selectMDiskbyPoolsandright-clicktheMDiskandselectQuorum>ModifyQuorumDisk.ThenewIPquorumapplicationisdisplayedinthetableofdetectedapplications.YoucanalsousethelsquorumcommandonthesystemCLItoverifythattheIPquorumapplicationisconnectedandistheactivequorumdevice.IfyouwanttomodifytheMDiskthatareusedforquorumbyusingthecommand-lineinterface,usethechquorumcommand.Parenttopic:HYPERLINK\o"AquorumdiskisanMDiskoramanageddrivethatcontainsareservedareathatisusedexclusivelyforsystemmanagement."Quorumdisk5.4ManualquorumdiskoverrideinaHyperSwapsystemAmanualquorumdiskoverrideisrequiredwhenyouexperiencearollingdisaster.Inraresituations,thesystemissubjecttowhatisreferredtoasarollingdisaster.Arollingdisasteroccurswhenanincidenthaswidescope,anditseffectsarefeltinmultiplestepsoveranextendedtimeperiod.Thefollowingexamplescenariodescribesarollingdisasterandshowshowtorecoverfromthatrollingdisaster.Anexampleofarollingdisasteroccurswhenthefollowingsituationistrue:Thelinkbetweenthetwositesfails,atwhichpointonesiteusestheautomaticquorumfeaturetocontinueoperation.Thesystemsitethathascontrolofthequorumdiskfails(duetoapoweroutage,forexample).ThisexampleleavesthesecondsiteastheonlysitethatispotentiallycapableofcontinuingdataI/O.However,itisunabletodosountilitgainscontrolofthequorumdisk.TheMDisksinthesecondsitestop.Nodesatthesitedisplaythenodeerror551,indicatingthataninsufficientnumberofnodesareavailabletoformaquoruminaHyperSwap?systemconfiguration.Inthisscenario,youcanrunthesataskoverridequorumcommandtooverridetheautomaticquorumdiskselectionandcreateanewsystemthatcontainsthenodesinthesecondsite.Note:Ifafabricdisruptionoccurswhilethesataskoverridequorumcommandisrunning,itispossiblethatasubsetofthenodeswillupdatetheircluster(system)ID.Theupdatednodesdisplaythenodeerror550;thenodesthatwerenotupdateddisplay551andthenodesareassignedtotwodifferentsystems.Inthissituation,youcanrunthesataskoverridequorumcommandagainononeofthenodesthatreportedtheerror551.Thiscommandupdatesallthenodesinthetwosystemswithanewcluster(system)ID.Youcanthenrecoverdata.5.5EnforcingconditionsforaquorumYoumustrunthechsystem-topologyhyperswapcommandaspartoftheinstallationprocessforthesystemtomakethesataskoverridequorumcommandavailableifarollingdisasteroccurs.Thesataskoverridequorumcommandisnotavailableinsystemsthatdonothavethetopologysettohyperswap.Beforeyoucanusethecommand,thefollowingprerequisitesmustbemet:AllI/Ogroupswithtwonodesareassignedwithonenodeinsite1andtheotherinsite2.AllstoragesystemswithMDisksmusthavetheirsitedefined.Whentheseprerequisitesaremetandautomaticquorumselectionisenabled,thesystemattemptstoassignonequorumdiskwithinallthreesites.IfasitedoesnothaveanMDisksuitabletobeaquorumdisk,aquorumdiskisnotassignedtoit.Note:Afterthechsystem-topologyhyperswapcommandisrun,youcannotalterthesiteassignmentofanycontrollerexceptwherethatcontrollerisanewcontrollerthathasonlyunmanagedMDisks.Itwillalsonotallowsitesettingsfornodes.Thisenforcementisrequiredtoensurethatthesystemoperatescorrectlytoallowthesataskoverridequorumcommandtooperatecorrectly.Whenyourunthechsystem-topologystandardcommand,itagainispossibletoalterthesitesettingsfornodesandcontrollers.However,thiscommanddisablestheoverridequorumfeature.Therefore,aimtorunchsystem-topologyhyperswapwhenyoucompleteyourchangestoreenablethissupport.六、HyperSwapconfigurationwithoutusinginterswitchlinksThemostsimpleIBM?HyperSwap?configurationisbuiltbyattachingeachcontrolenclosure