Embed Size (px)
Citation preview
Design and Implementation of a Linux
SCSI Target for Storage Area Networks
Ashish A. Palekar Anshul Chaddha,Trebia Networks Narendran Ganapathy,33 Nagog Park Robert RussellActon, MA 01720 UNH-IOL
Durham, NH –[email protected] {achadda, ng3, rdr}@iol.unh.edu
Overview• Motivation and Objectives• Architecture• Design Details
– User Space Target Emulator– Kernel Space Target Emulator
• Implementation Issues• Configuration Tool• Applications• Conclusions and Future Work
Motivation and Objectives
• Internet + E-Commerce = Data• Storage Area Networks – Concept• Emergence of Protocols
– Fibre Channel– SEP (SCSI Encapsulation)– iSCSI (Internet SCSI)– iFCP– Infiniband
• Linux as a SCSI Target ?
SCSI Protocol Overview
SCSI Initiator Mid-LevelUser Space
Kernel SpaceSD
disksBlock device
Lower Level
SRcdrom/dvd
Block device
STtapesChar
device
SGgeneric
Char device
Upper Level
Mid Level
SCSI Unifying LayerConversion of command requests into SCSI requests.Hands off these requests to the low level driver.
Host Bus Adapter Drivers
Drivers for Non-SCSI
buses
SCSI Initiator and Target
Software Design Aspects
Basic Code Paths:1. Registration /
Deregistration2. SCSI Read Type
Commands3. SCSI Write Type
Commands4. SCSI Task Management
Commands5. Configuration of the SCSI
Target
Step One: User Space Target Emulator
SCSI Mid-level
SEP Initiator
SEP Target Front-end
interpret_cmdhandle_SEP_connectionscsi_server
SCSI Target Emulator
handle_file_iohandle_generic_cmdhandle_SCSI_cmd
sep_disk_file
scsi_generic
API
TCP/IP Connection
SCSI Mid-level
qlogicfc driver (for QLA 2200)
Fibre Channel Disk (Seagate)
SD disks (Block
devices)
user spacekernel space
User Level Application to generate SCSI activity e.g., cp
Registration Interface
Deregistration Interface
Handling a SCSI Read Type Command
Handling a SCSI Write Type Command
“Processing” a SCSI Command“Processing” – different handle_cmd functions1. I/O to and from memory MEMORYIO
- Return junk data on READ commands- Drop data from WRITE commands- Used for protocol performance testing
2. I/O to and from a file FILEIO- Open a file on the local system- Block READs and WRITEs to the file- “Safe” mode for driver testing- Abstract view IDE SCSI conversion
3. I/O to and from a disk GENERICIO/DISKIO- “Bridge” mode of operation- Protocol conversion between different SCSI
Transport Protocols
“Processing” a SCSI Command
DISKIO
GENERICIO
Handling a SCSI Task Management Command
Implementation Details• Initiator side:
– Existent Fibre Channel Initiator used (QLogic ISP 2200 A)
– Front End Initiator drivers – SEP, iSCSI written
• Target Side:– Developed the SCSI Target Mid-Level– Developed Front End Target Drivers for
– Fibre Channel (QLogic ISP 2200 A)– SEP– iSCSI – draft ’06’ – upgrading to ’09’
– Linux TCP/IP stack used …
Target Configuration• Need
– Statistical information– Configuration Needs for individual driver– Interface for complex SAN management
tools• Mechanism
– “proc” file system• Usage
– iSCSI Login Negotiation Parameters
Conclusions• Input to Standards Bodies (IETF)
– Development of Frame Structure– Simplification of Login Process– Identifying potential performance issues– iSCSI State Diagram
• SCSI Target Mid-Level - Generic uses– IDE disks used as SCSI drives– Linux as a bridge
• Implementations used at Interop plugfests
Future/Current Work• Making STML/FETDs more robust• Upgrading iSCSI FETD to current
versions• IP-sec and Authentication (CHAPs)
for iSCSI• Submit for inclusion in kernel• “Storage Virtualization” interface• “Command Processing”
Acknowledgements
• SUN Microsystems• EMC• Trebia Networks• InterOperability Lab, UNH
Thank you
Downloads:http://www.iol.unh.edu/consortiums/fc/fc_li
nux.html
