Storage virtualisation happens at many levels between the disk tracks and sectors and what an application or operating system sees. Tom Clark takes us through this before launching into the modern era with virtualisation of storage accessed across a network. He manages to describe how disk I/O is managed and how different aspects of it are virtualised as he covers the ground from tracks and sectors, through controllers, RAID cards, and access protocols such as SCSI and Fibre Channel.

There are useful descriptions of volumes, of LUNs, of file systems, with Unix and Windows compared. Clark discusses storage abstraction, how physical devices and their characteristics are treated to make storage more usable.

He discusses virtualisation of SANs and of NAS storage, also virtual tape. The bulk of the book discusses disk array virtualisation. Naturally the in-band and out-of-band concepts are discussed. He also looks closely at the place where virtualisation is carried out: the host server; inside the fabric in an intelligent device; or at the array.

The topic of virtualisation services is addressed and he touches on heterogeneous mirroring and data replication, point-in-time data snapshots and hierarchical storage management. Virtualised file systems are described. He looks at storage automation and virtualisation and finishes with a discussion of the storage utility.

He explains that many descriptions of virtualisation are clouded because people discuss storage services, such as replication, that don't actually need virtualisation. After having read this book you can see through the hype that may be put out about virtualisation products and get to the nitty-gritty.

This book will enable you to classify the various virtualisation approaches from suppliers and understand the differences between them. It will help you understand where virtualisation could be applied in your storage infrastructure and what would be involved in implementing it. The benefits are made apparent and so are the additions that will need to be made to your infrastructure.

Clark, although working for a vendor with a particular approach, seems to be objective and neutral in his discussions. No one approach has yet won out and there is a case to be made for each of the approaches covered.

Tom Clark has written two previous popular and authoritative books - on Designing Storage Area Networks and on IP SANs: A Guide to iSCSI, iFCP and FCIP Protocols for Storage Area Networks. This third book is at least as good as the previous two and probably better.

Storage virtualisation is becoming mainstream and it will probably be the case that virtualising storage into logical pools will become as common tomorrow as RAID storage is today. This book is a great way to learn all about the topic and be better prepared to deal with it.

OUR VERDICT

To get a comprehensive and detailed account of storage virtualisation read this book.