iSCSI: The Universal Storage Connection

by John L. Hufferd

Overview

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.

Product Details

ISBN-13:	9780134171821
Publisher:	Pearson Education
Publication date:	01/09/2015
Sold by:	Barnes & Noble
Format:	eBook
File size:	4 MB

About the Author

John L. Hufferd has been a key technical leader and manager within IBM for more than thirty-five years and currently directs projects dealing with networks, storage, and SANs. He is the technical coordinator for the iSCSI track of the IPS workgroup in the IETF standards association.

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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.


Preface.


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.

SCSI Over TCP/IP.

Measurements.

Cisco and IBM's Joint Effort.

iSCSI and IETF.

The End of the Story.

4. An Overview of iSCSI.

TCP/IP.

TCP/IP Summary.

iSCSI-Related Protocol Layers.

Protocol Summary.

Sessions.

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.

Sequencing.

Resending Data or Status.

Recap.

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.

MIB AND SNMP.

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.

TUF/FIM.

14. iSCSI Summary and Conclusions.

Summary.

iSCSI Development History.

Conclusions.

iSCSI Network Management.

Ease of Administration.

Backup and Disaster Preparation.

Performance.

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.

NOP-In PDU.

NOP-Out 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-In PDU.

SCSI Data-Out PDU.

SNACK Request PDU.

Resegmentation.

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.

AuthMethod Keys.

DataDigest.

DataPDUInOrder.

DataSequenceInOrder.

DefaultTime2Retain.

DefaultTime2Wait.

ErrorRecoveryLevel.

FirstBurstLength.

HeaderDigest.

IFMarker.

IFMarkInt.

ImmediateData.

InitialR2T.

InitiatorAlias.

InitiatorName.

MaxBurstLength.

MaxConnections.

MaxOutstandingR2T.

MaxRecvDataSegmentLength.

OFMarker.

OFMarkInt.

SendTargets.

SessionType.

TargetAddress.

TargetAlias.

TargetName.

TargetPortalGroupTag.

X-<VendorSpecificKey>.

X#<IANA-registered-string>.

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

Preface

This book is a guide to understanding Internet SCSI (iSCSI) and where it fits in the world. It contains discussions of the marketplace where appropriate and of some 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, that is, a carrier of the SCSI protocol, there is no involved discussion of SCSI itself. Many parts of the book are general enough that a thorough knowledge of SCSI is not needed. There are, however, more detailed parts of the book where SCSI knowledge would be helpful.

I wrote this book to provide both the manager and the technician with a useful understanding of the technology. Product marketing and strategy professionals should also find the information useful and meaningful. The technician should view this book as a primer, in which the iSCSI technology is discussed with enough depth that the IETF iSCSI documents should be readily understandable. Those who want 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 IETF iSCSI drafts/standards documents.

The book attempts to service divergent readers by ensuring that, when a chapter contains in-depth technical content, the reader will be so advised by a "To the Reader" commentary, which is flagged with the iSmiley face. If appropriate, readers may skip forward to a topic or the Chapter Summary (also marked with the iSmiley face) for the highlights.

Organization

The book begins with a general background of the market and an answer to why iSCSI is of interest. A taxonomy of the various markets is given, along with an explanation of how iSCSI fits into them. This is followed by a short history of iSCSI so that the reader can get a sense of what propelled its development.

Next the book heads into the technology itself, with an overview that includes iSCSI layering. This shows the use of the underpinning TCP/IP technology, the concept of a session, and the structure of the message units. Various other key concepts are introduced here to ensure that the reader knows not only the importance of data integrity to storage technology, but also that new hardware is being introduced specifically to address bandwidth and latency issues. A few pages are spent explaining the iSCSI naming conventions, because of their 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 processes are key 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.

One chapter is dedicated to merging 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 in a very technical discussion. The detail and technical depth build from that point to the end of the book. Finally the reader is taken through the various companion technologies that iSCSI uses to complete its suite of capabilities.

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

Of course, there is an overall summary that considers expectations for the future.

Appendix A contains most of the truly technical details of the iSCSI protocol. The message units are presented in alphabetical order for ease of reference. Appendix B contains a compact listing of the various negotiation keywords and values.

Appendix C goes into the relationship of iSCSI to the SCSI architecture. It explains the logical model and its consequences. Appendix D contains the details of the key=value field encodings of numbers, characters, and bits.

Readers may forget from time to time the meanings of various iSCSI and SCSI terms, so a glossary is presented in Appendix E. As a further aid I have included in Appendix F the various acronyms used throughout this book and many of the referenced documents, especially the base IETF iSCSI drafts.

Finally, Appendix G contains the various reference sources, along with their Web page locators (in most cases). Speaking of references, bracketed citations, such as SAM2, are fully referenced in this appendix.

In iSCSI, serial numbers are always incremented and compared in what is called a 32-bit serial number arithmetic. This is a way to determine, when serial numbers wrap around, if those numbers are greater or less than other serial numbers.

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