Design and Implementation of a Linux SCSI Target for Storage Area NetworksAshish A. PalekarAnshul Chaddha,Trebia Networks Narendran Ganapathy,33 Nagog Park Robert RussellActon, MA 01720UNH-IOL Durham, NH 03824apalekar@trebia.com{achadda, ng3, rdr}@iol.unh.edu

OverviewMotivation and ObjectivesArchitectureDesign DetailsUser Space Target EmulatorKernel Space Target EmulatorImplementation IssuesConfiguration ToolApplicationsConclusions and Future Work

Motivation and ObjectivesInternet + E-Commerce = DataStorage Area Networks ConceptEmergence of ProtocolsFibre ChannelSEP (SCSI Encapsulation)iSCSI (Internet SCSI)iFCPInfinibandLinux as a SCSI Target ?

SCSI Protocol Overview

SCSI Initiator Mid-Level

SCSI Initiator and Target

Software Design AspectsBasic Code Paths:Registration / DeregistrationSCSI Read Type CommandsSCSI Write Type CommandsSCSI Task Management CommandsConfiguration of the SCSI Target

Step One: User Space Target Emulator

Registration Interface

Deregistration Interface

Handling a SCSI Read Type Command

Handling a SCSI Write Type Command

Processing a SCSI CommandProcessing different handle_cmd functionsI/O to and from memory MEMORYIOReturn junk data on READ commandsDrop data from WRITE commandsUsed for protocol performance testingI/O to and from a file FILEIOOpen a file on the local systemBlock READs and WRITEs to the fileSafe mode for driver testingAbstract view IDE SCSI conversionI/O to and from a disk GENERICIO/DISKIOBridge mode of operationProtocol conversion between different SCSI Transport Protocols

Processing a SCSI CommandDISKIOGENERICIO

Handling a SCSI Task Management Command

Implementation DetailsInitiator side:Existent Fibre Channel Initiator used (QLogic ISP 2200 A)Front End Initiator drivers SEP, iSCSI writtenTarget Side:Developed the SCSI Target Mid-LevelDeveloped Front End Target Drivers forFibre Channel (QLogic ISP 2200 A)SEPiSCSI draft 06 upgrading to 09Linux TCP/IP stack used

Target ConfigurationNeedStatistical informationConfiguration Needs for individual driverInterface for complex SAN management toolsMechanismproc file systemUsageiSCSI Login Negotiation Parameters

ConclusionsInput to Standards Bodies (IETF)Development of Frame StructureSimplification of Login ProcessIdentifying potential performance issuesiSCSI State DiagramSCSI Target Mid-Level - Generic usesIDE disks used as SCSI drivesLinux as a bridgeImplementations used at Interop plugfests

Future/Current WorkMaking STML/FETDs more robustUpgrading iSCSI FETD to current versionsIP-sec and Authentication (CHAPs) for iSCSISubmit for inclusion in kernelStorage Virtualization interfaceCommand Processing

AcknowledgementsSUN MicrosystemsEMCTrebia NetworksInterOperability Lab, UNH

Thank you

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