Live WAN VM Migrationppt生活migrationppt万VM.ppt

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Implementation–BulkXfer
TheVM’sdiskimageistransferredfromthesourcetothedestination.
XenoServersplatformsupportscopy-on-writealongwithimmutabletemplatediskimages,sowecanjusttransferthechanges,ratherthanthewholeimage.
Implentation–XenMigration
Thesystemherereliesonthebuilt-inmigrationmechanismofXen.
XenlogsdirtymemorypagesandcopiesthemtothedestinationwithoutstoppingthesourceVM.
Eventually,wewillhavetopausethesourceandcopytheremainingmemorypages.
ThenwestartupthemigratedVM.
Implementation-Intercepting
TheblkfrontdevicedrivercommunicateswiththededicatedstorageVMviaringbuffer.
Theblktapframeworkinterceptsrequests,butdoesitinuserspace.
Onceadiskrequestmakesittothebackend,itisbothcommittedtothediskandsenttothemigrationclient.
Theclientthenpackagesthewriteupasadelta.
Implementation-Application
Afterthebulktransfer,andinparallelwiththeXentransfer,thedeltasaretransferredandappliedtothemigratedVMbythemigrationdaemoninthestorageVMatthedestination.
IfthedeltaqueuebecomesemptyandtheXenmigrationisfinished,I/Orequestsareputonholduntiltheapplicationofthecurrentcropofdeltasisfinished.
TheauthorsfoundthatdeltaapplicationwasnormallyfinishedbeforeXenmigration,addingzerotimetotheoverallmigration.
Implementation–WriteThrottling
IftheVMattemptstocompletemorewritesthanagiventhresholdvalue,futurewriteattemptsaredelayedbytheblockdriver.
Thisprocessrepeats,withthedelayandthresholddoublingeachtime.
Experimentally,16384isasuitablethresholdwithadelayof2048μsalsobeinggood.
Enforcementisseparatedfrompolicyforextensibility.
Implementation–WANRedirection
IftheIPoftheVMchanges,weuseIPtunnelingandDynamicDNStopreventdroppednetworkconnections.
JustbeforethesourceVMispaused,anIPtunneliscreatedfromthesourcetodestinationusingiproute2.
OncethedestinationVMiscapableofrespondingtorequestsatitsnewIP,DynamicDNSforwardstherequeststothenewIP.
Packetsthatarriveduringthefinalstageofmigrationaresimplydropped.
OncenoconnectionsexistthatusetheoldIP,thetunnelistorndown.
Practically,thisworksbecause:
Thesourceserveronlyneedstocooperateforashorttime,mostnetworkconnectionsareshort-livedandifnothingelse,it’snoworsethanwhatyougetiftheVMdoesn’teventry.
Evaluation-Metrics
Wanttoevaluatethedisruptionofthesystem,asperceivedbyusers.
Spoiler:Resultslookgood.
Wanttoshowthesystemhandlesdiabolicalworkloads,definedinthispaperasbeingheavydiskaccessors,ratherthanheavymemoryaccessors.
Downtime:TimebetweenpausingtheVMonthesourceandresumingonthedestination.
DisruptionTime:Timeduringwhichclientsobserveareductioninserviceresponsiveness.
AdditionalDisruption:Differencebetweendisruptiontimeanddowntime.
Migrationtime:TimefrommigrationrequesttorunningVMatdestination.
NumberofDeltasandDeltaRate:Howmanyfilesystemchangesandhowoftentheyoccur.
Eval–WorkloadOverview
Webserverservingstaticcontent,servingdynamicwebapplicationandvideostreaming.
ChosenforrealisticusagescenariosandbecausetheyneatlytrifurcatethespectrumofdiskI/Opatterns:
Dynamicappgenerateslotsofburstywrites
Staticworkloadgeneratesamediumamountofconstantwrites
Streamingvideocausesfewwrites,butisverysensitivetodisruption.
Eval–ExperimentalSetup
Threehosts
,4GBDDRRAM,mirroredRAIDarrayofU320SCSIdisks.
ThemigratedVMwasprovidedwith512MBRAMandasingleCPU.
Allhostswereconnectedbya100MbpsswitchedEthernetnetworks.
ThemigratedVMwasrunningDebianona1GBext3disk.
HostCistheclient.
ToemulateWANtransfers,trafficshapingwasusedtolimitthebandwidthto5Mbpswith100msoflatency.
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