SCSI: The New Universal Method of Connecting to Storage
J. Hufferd · Addison-Wesley Longman Publishing Co., Inc. eBooks · 2002
From the Book: 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 indepth 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.)