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Reviewer: David Gary Hill

Information assets are universally recognized as being vital to an enterprise. The unchecked growth of these assets has at times led to unmanageable complexity in managing and storing that information. In recent years, information technology organizations have been introducing new technologies, such as storage area networks, to attack the ongoing problem. Storage virtualization is seen as an enabling technology that works with these new technologies to help deal with the simplification of the management of data storage, thereby leading to lower administrative costs. However, storage virtualization has been seen as a complex subject, one in need of a comprehensive treatment to better facilitate its understanding. This book is a work that gives the subject of storage virtualization the treatment it deserves. The book is technical, and is aimed at readers with a solid background in data storage. The introductory chapter provides an overview of storage virtualization. Storage virtualization logically abstracts physical storage systems, and thereby hides the complexity of the actual storage devices from the process of managing them. Chapters 2 through 4 lay the foundation for understanding the relationship between what the user sees and what goes on in the background to make virtualization happen. Chapter 2 focuses on files and records; chapter 3 focuses on data on disk, including a discussion of blocks and the ubiquitous redundant array of independent disks (RAID); and chapter 4 discusses the plumbing of storage interconnects that provides the paths to storage. Chapters 5 through 9 provide strategies for implementing storage virtualization. Chapter 5, on abstracting physical storage, states that the secret recipe for virtualization is the process of mapping logical block addresses to virtual block addresses. The next three chapters describe the three places where virtualization can be implemented. The first is host-level virtualization, such as the use of logical volume managers. The second is array-based virtualization, where the virtualization can either be at the level of discrete disks or at the level of entire storage systems. The third is fabric-based virtualization, where virtualization can be located in the switch of a storage area network. Chapter 9 discusses virtualization appliances, including the difference between in-band and out-of-band strategies for implementing virtualization. Chapter 10 discusses storage management services that can work in conjunction with virtualization across a pool of heterogeneous storage assets (for example, storage products from multiple vendors). Those services include heterogeneous local mirroring, where the primary storage and the secondary mirror do not have to be the same brand; heterogeneous data replication?that is, remote mirroring; point-in-time snapshots; and hierarchical storage management. Chapter 11 covers virtualized file systems, which enable file?not just block?virtualization, and improve file sharing. Chapter 12 discusses the virtualization of tape systems. Chapter 13 covers the important relationship between virtualization and storage automation for potentially simplifying storage management. Policy-based management is central to that automation process. The author covers the important work that the Storage Networking Industry Association (SNIA) is doing with its storage management interface specification (SMI-S) to define a common management interface for storage. In addition, both application-aware storage virtualization and virtualization-aware applications are addressed. The final chapter, chapter 14, covers the storage utility, which addresses how access to storage can be made ubiquitous. A technical work can be used as an aid to comprehension and understanding, as a source for reexamining particular points of interest in the future, and as a springboard to help determine a future course of action. Apart from numerous graphics, the book offers some features that make it useful for each of these three purposes. Each chapter ends with a bulleted list of major points from the chapter by topic, which reinforces the points made in the chapter and makes future reference easier. In addition to a standard index and bibliography, there is an extensive and comprehensive glossary. Finally, there are three useful appendices. The first is on industry resources, and the second is a list of vendor resources. A unique feature is an appendix that gives several other writers the opportunity to express their opinions on virtualization; this is a useful addition, which allows the reader to compare and contrast these viewpoints with what the author has covered in the book. Online Computing Reviews Service