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iSCSI: The Universal Storage Connection: The Universal Storage Connection

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iSCSI: The Universal Storage Connection: The Universal Storage Connection


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  • Copyright 2003
  • Dimensions: 7-3/8" x 9-1/4"
  • Pages: 368
  • Edition: 1st
  • Book
  • ISBN-10: 0-201-78419-X
  • ISBN-13: 978-0-201-78419-0

iSCSI: The Universal Storage Connection is an informative overview and in-depth guide to the emerging iSCSI standard, the technology that enables data storage, access, and management over networks, intranets, and the Internet. The iSCSI protocol reduces the total cost of ownership of shared storage solutions and enables an organization to tie together disparate systems and data, including both server class systems and laptop and desktop systems. Numerous leading technology companies, including IBM®, Cisco Systems®, and Intel®, are currently supporting iSCSI initiatives.

Written for network and data storage professionals, this comprehensive book introduces iSCSI and explores its growing role within the data storage industry. It describes each element of the technology in detail—from session establishment through error handling—and examines the relationship between iSCSI and the SCSI protocol from which it evolved.

Specific topics discussed include:

  • iSCSI's use in small office, midrange, and high-end settings
  • TCP/IP fundamentals, and how they apply to iSCSI
  • The importance of data integrity
  • New hardware that addresses bandwidth and latency issues
  • iSCSI naming conventions
  • The establishment of a communication path between the host system and storage controller
  • Commands and data sequencing
  • Control of the flow of commands
  • Task management
  • Error handling
  • Companion technologies, including discovery and security processes
  • Backup and disaster preparation
  • iSCSI performance issues

In addition, the book includes an explanation of the technologies that hardware vendors are implementing to permit direct memory placement of iSCSI messages without additional main processor involvement.

A helpful icon appears throughout the book, mapping out appropriate reading tracks based on your technical level.

Comprehensive, clearly written, and organized for easy access, this iSCSI handbook serves as both an excellent starting point for those involved in data storage solutions and a guide to understanding the technically detailed Internet Engineering Task Force (IETF) iSCSI Standards document.

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The Value and Position of iSCSI

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Table of Contents

(NOTE: Each chapter, except Chapter 1, begins with To the Reader and all chapters conclude with a Summary.

Credits and Disclaimer.


1. The Background of SCSI.

SCSI BUS Interconnect.

Fibre Channel Interconnect.

iSCSI Interconnect.

File Servers and NAS.

2. The Value and Position of iSCSI.

The Home Office.

The Home Office and Serial ATA Drives.

The Small Office.

The Midrange.

The High End.

The Campus.

The Satellite.

The At-Distance Site.

The Central Site.

FC and iSCSI.

3. The History of iSCSI.



Cisco and IBM's Joint Effort.


The End of the Story.

4. An Overview of iSCSI.


TCP/IP Summary.

iSCSI-Related Protocol Layers.

Protocol Summary.


Session Summary.

Protocol Data Unit (PDU) Structure.

PDU Structure Summary.

iSCSI and TOE Integration on a Chip or HBA.

TOE Integration Summary.

Checksums and CRC (Digests).

Checksum and CRC Digest Summary.

Naming and Addressing.

Details of Naming and Addressing.

Naming and Addressing Summary.

5. Session Establishment.

Introduction to the Login Process.

Login and Session Establishment.

Login PDUs.

The Login Request PDU.

The Login Response PDU.

iSCSI Sessions.

Authentication Routines.

Login Keywords.

Keywords and the Login Process.

Discovery Session.

6. Text Commands and Keyword Processing.

Text Requests and Responses.

PDU Fields.

Text Keywords and Responses.

Rules for Key=Value Pairs.

Rules for Keyword Value Negotiation.

Rules for Negotiation Flow.

Rules for Negotiation Failure.

7. Session Management.

Initiator Session ID.

Connection Establishment.

Data Travel Direction.


Resending Data or Status.


8. Command and Data Ordering and Flow.

Command Ordering.

Command Windowing.

Initiator Task Tag.

Design Example: Direct Host Memory Placement.

Data Ordering.

Target Transfer Tag.

Data Placement (A Form of RDMA).

9. Structure of iSCSI and Relationship to SCSI.

iSCSI Structure and SCSI Relationship.

SCSI Nexus.

10. Task Management.

Tagged and Untagged Texts.

11. Error Handling.

Error Recovery Levels.

Error Recovery Level 0.

Error Recovery Level 1.

Header Digest Recovery at the Initiator Side.

Header Digest Recovery at the Target Side.

Data Digest Recovery.

Error Recovery Level 2.

12. Companion Processes.

Boot Process.

Discovery Process.

Discovery Using Administrative Specifications.

Discovery Using SendTargets.

Discovery Using the Service Location Protocol.

Discovery Using iSNS.

Security Process.

To the Reader.

IPsec Features.

Access Control Lists.


13. Synchronization and Steering.

Main Memory Replacement.

Errors and Congestion.

Missing TCP Segments and Marking.

Fixed-Interval Markers.

FIM Pointers.

Marker Implementation.

FIM Synchronization Scheme.

TCP Upper-Level-Protocol Framing (TUF).

The TUF Scheme.

The TUF Header.

Advantages and Disadvantages.


14. iSCSI Summary and Conclusions.


iSCSI Development History.


iSCSI Network Management.

Ease of Administration.

Backup and Disaster Preparation.


The Future.

Summary of Conclusions.

Appendix A: iSCSI Function PDUs.

Serial Number Arithmetic.

Asynchronous Message PDU.

Login Request PDU.

ISID, TSIH, and CID Values.

Login Response PDU.

Logout Request PDU.

Notes on the Logout Request PDU.

Implicit Termination of Tasks.

Logout Response PDU.



Ready to Transfer (R2T) PDU.

Notes on the R2T PDU.

Reject PDU.

Notes on the Reject PDU.

SCSI (Command) Request PDU.

SCSI (Command) Response PDU.


SCSI Data-Out PDU.

SNACK Request PDU.


Notes on the SNACK Request PDU.

Task Management Function Request PDU.

Notes on the Task Management Function Request PDU.

Task Management Function Response PDU.

Notes on the Task Management Function Response PDU.

Text Request PDU.

Text Response PDU.

Appendix B: Keys and Values.


AuthMethod Keys.





























Appendix C: SCSI Architecture Model.

SCSI-iSCSI Mappings.

Consequences of the Model.

I-T Nexus State.

SCSI Mode Pages.

Appendix D: Numbers, Characters, and Bit Encodings.

Text Format.

Appendix E: Definitions.

Appendix F: Acronyms.

Appendix G. References and Web Pointers.

Basic References for iSCSI.

References for SCSI-Related Items.

References for iSCSI Security and IPsec/IKE.

References That Indirectly Affect iSCSI.

Index. 020178419XT10112002


This book is a guide to understanding Internet SCSI (iSCSI) and where it fits in the world. It contains both discussions of the market places where it is appropriate as well as some of it technology competitors—such as Fibre Channel. However, mostly there will be positioning of the various technologies to emphasize their appropriate strengths. iSCSI, is based on such a ubiquitous network technology (TCP/IP) that it seems to play in many different areas that are currently dominated by other technologies. Therefore, one needs to view all iSCSI capabilities and determine its applicability to the area in which the reader is interested.

Since iSCSI is only a transport, a carrier of the SCSI protocol, there is not an involved discussion of SCSI itself. Many parts of the book are general enough so that a thorough knowledge of SCSI is not needed. There are, however, more detail parts of the book where knowledge of SCSI would be helpful.

This book is being written to provide both the manager and the technician a useful understanding of the technology. Likewise, product marketing and strategy professionals should find the information useful and meaningful to their jobs.

The technician should view this book as a primer, which discusses the iSCSI technology with enough depth, that the details found in the IETF iSCSI Standards document should be readily understandable. Anyone that is planning to understand and build a product based on iSCSI should find this book to be a must read, especially if they plan to dive down into the details of the iSCSI Standard document.

The book attempts to service these divergent readers by ensuring that when the chapter contains in depth technical content, the reader will be so advised by a commentary under a subtitle of "Reader Suggestions." And these suggestions are flagged with the iSmiley face.

Then if appropriate the reader may skip forward to the Chapter Summary to acquire the highlights of the chapter.

Book Organization

The book begins by giving a general background of the market, and why iSCSI is of interest. A taxonomy of the various markets is listed along with a positioning of iSCSI into those markets explaining how it fits into that array of opportunities. This is followed by a short history of iSCSI so that the reader can get a sense of what propelled this technology to be developed.

Then the book heads into the technology itself showing an overview of the technology, and its layering. This shows both the use of the underpinning TCP/IP technology, the concept of a session, as well as the structure of the message units. Various other key concepts are also introduced here to ensure that the reader knows not only the importance of data integrity to storage technology but also that there is new hardware being introduced to specifically address bandwidth and latency issues. Then a few pages of text are spent explaining the iSCSI naming conventions, because it is of major significance to the use of the technology.

Following the discussion of iSCSI naming conventions, the book takes the reader through the login process and the identification and option negotiation process. These steps are key to iSCSI in the establishment of a communication path between the host system and the storage controller.

The process of sequencing the commands and data, as well as controlling the flow of commands and data is reviewed.

A chapter is also dedicated to merging the iSCSI concepts with SCSI concepts, by depicting where the various named entities are located. This is perhaps the most tedious chapter, even though not deep in technical content.

The various forms of task and error management are explained, which is intended as a very technical discussion.

The detail and technical depth builds towards the end of the book, through the chapter on error handling. Then, the reader is taken through the various companion technologies which iSCSI uses to complete its suite of capabilities.

The main part of the book then concludes with a special technology explanation of what hardware vendors are doing to permit direct memory placement of iSCSI messages without additional main processor involvement.

And of course there is an overall summary and expectations for the future.

Following the book summary is appendix A, which contains most of the real technical details of the iSCSI protocol. The message units are detailed in alphabetical order for ease of reference, followed by Appendix B, which contains a compact listing of the various negotiation keywords and values.

Appendix C goes into the details of the relationship of iSCSI to the SCSI Architecture. It explains the logical model, and the consequences of the model. Appendix D contains the details of the key=value field encodings of Numbers, Characters, and Bits.

The reader may forget from time to time the meanings of various iSCSI and SCSI terms, so their definitions (with more detail then the main part of the book) are included in Appendix E. And as a further aid to the reader we have included in Appendix F the various Acronyms used throughout this book and many of the referenced documents, especially the base IETF iSCSI Draft Standard.

Appendix G contains the various reference sources, along with their Web Page locators, where possible.

When a word in this book is surrounded by square brackets, such as SAM2, this denotes that you will find a reference to this document in Appendix G.

In iSCSI when serial numbers are incremented and compared, they are always done in what is called a 32-bit Serial Number arithmetic. Refer to Appendix A for a quick overview and to RFC1982 for the details of Serial Number arithmetic. (It is a way to determine—when serial numbers wrap around—if they are greater or less then other serial numbers.)



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