iSCSI_协议介绍及实施方案

CiscoSystems,Inc.AllcontentsareCopyright©1992–2002CiscoSystems,Inc.Allrightsreserved.ImportantNoticesandPrivacyStatement.Page1of15WhitePaperIntroductiontoiSCSIExecutiveSummaryThiswhitepaperprovidesabasicworkingknowledgeoftheInternetSmallComputerSystemsInterface(iSCSI)protocol.iSCSIisanSCSItransportprotocolformappingofblock-orientedstoragedataoverTCP/IPnetworks.ThepaperfocusesprimarilyoniSCSI,thereforesomebackgroundinSCSIandstorage-areanetwork(SAN)protocolsandarchitecturesisrecommended.Additionalwhitepapersthatcovertheseotherareasarereferencedattheendofthisdocument.InformationontheiSCSIprotocolprovidedinthisdocumentisbasedontheInternetEngineeringTaskForce(IETF)IPStorage(IPS)iSCSIdraft10.Foradditionaldetails,thisdocumentcanbereferencedviatheURLprovidedinthereferencesattheendofthedocument.ThispaperincludesabreakdownoftheiSCSIprotocolandprocesses,iSCSIsecurityandmanagementconsiderations,andsomebasicimplementationinformation.Additionally,termsandacronymsaredefinedastheypertaintotheiSCSIprotocol.iSCSIinPerspectiveBasicConceptofiSCSIConceptually,iSCSI+TCP+IPprovideanequivalentofLayer3/4networktransport,ratherthanalternativesofeitherparallelSCSIcableorFibreChannelProtocol(FCP)(SCSIoverFibreChannel).ThebasicideaofiSCSIistotakeadvantageoftheinvestmentinexistingIPnetworkstofacilitateandextendSANs.ThisisaccomplishedbyusingtheTCP/IPprotocoltotransportSCSIcommandsanddatabetweenhostandSANnodes.TraditionallySANshaverequiredaseparatededicatedinfrastructuretointerconnecthostsandstoragesystems.TheprimarymeansfortheseinterconnectionsareFibreChannelnetworksthatprovidetheSCSItransport.TheresultisthatseparateparallelnetworkshavetobebuilttosupportIPapplicationsandassociatedstorage.Additionally,FibreChannelcannotbetransportedoverlower-bandwidthWANnetworksinitsnativeform,thereforerequiresspecialhardwareandhandling.TheuseofiSCSIoverIPnetworksdoesnotnecessarilyreplaceaFibreChannelnetworkbutratherprovidesatransportforanIP-attachedhosttoreachFibreChannel-basedSANs.CiscoSystems,Inc.AllcontentsareCopyright©1992–2002CiscoSystems,Inc.Allrightsreserved.ImportantNoticesandPrivacyStatement.Page2of15IPnetworkinfrastructuresprovidemajoradvantagesforinterconnectionofserverstoblock-orientedstoragedevices.IPnetworksarecost-effective,andtheyprovidesecurity,scalability,interoperability,networkmanagement,andstoragemanagement.IPnetworkadvantagesinclude:•IPnetworksoffertheavailabilityofnetworkprotocolsandmiddlewareformanagement,security,andqualityofservice(QoS).•SkillsdevelopedinthedesignandmanagementofIPnetworkscanbeappliedtoIPSANs.TrainedandexperiencedIPnetworkingstaffsareavailabletoinstallandoperatethesenetworks.•IPnetworksoffereconomiesachievedfromusingastandardIPinfrastructure,products,andserviceacrosstheorganization.•iSCSIiscompatiblewithexistingIPLANandWANinfrastructures.•Distanceislimitedtoapplicationtimeout,notbyIPnetworks.ValueofiSCSIBybuildingonexistingIPnetworks,userscanconnecthoststostoragefacilitieswithoutadditionalhostadapters,betterutilizestorageresources,andeliminatetheneedforseparateparallelWANinfrastructures.BecauseiSCSIusesTCP/IPasitstransportforSCSI,informationcanbepassedoverexistingIP-basedhostconnectionstypicallyviaEthernet.Additionalvaluecanberealizedbybeingabletobetterutilizeexistingstorageresources.BecausehostscanutilizetheirexistingIP/Ethernetnetworkconnectiontoaccessstorageelements,itisnoweasiertoconsolidatestorageand,therefore,realizehigherutilization.Asmentionedpreviously,SANshaveinthepastrequiredspecialprovisionsforWANconnectivity.SignificantcostsavingscanberealizedbyutilizingexistingWANconnectionsforhoststoaccessstorageviaIP.OtherIPSANProtocolsItshouldbenotedthatthereareotherproposeddraftsfortransportingstoragetrafficoverIPnetworks.TheseincludeFibreChanneloverIP(FCIP),InternetFibreChannel(iFCP),andInternetStorageNameService(iSNS).Althoughtheseprotocolsareoutsidethescopeofthisdocument;additionalinformationonthemcanbefoundinthereferences.iSCSIStandardsTrackTheiSCSIdraftisoneofseveralprotocolsbeingworkedonbytheIPStorage(IPS),workinggroupintheIETF.ManyindustryleaderssuchasCisco,IBM,andHPareleadingtheeffortofstandardizingthedraft.Thecurrentreleaseisdraft-ietf-ips-iscsi-14datedJuly1,2002.ItisanticipatedthattheiSCSIdraftwillbesubmittedtotheInternetEngineeringSteeringGroup(IESG)forconsiderationasproposedstandardslaterthisyear.Numerousvendorsarecurrentlydevelopingproductstothecurrentdraftstandard.WhensettingupprestandardiSCSIsolutions,itisnecessarytodeterminewhichdraftavendor’sproduct(s)isbasedoninordertoachieveinteroperability.CiscoSystems,Inc.AllcontentsareCopyright©1992–2002CiscoSystems,Inc.Allrightsreserved.ImportantNoticesandPrivacyStatement.Page3of15FundamentalsofiSCSIThissectiondiscussesthevariouslayersandprocessesofiSCSIinordertobuildanoverallfunctionalunderstanding.Therefore,detailedpacketformatsandstructuresareintentionallyomitted.ThissectionfocusesoniSCSIspecifically,andthetransportofSCSIoverIP.However,abriefdiscussionofSCSIarchitectureisprovidedtoaidintheunderstandingofthisdocument.SCSIArchitectureSCSIstandsforSmallCompute