In "The Holy Grail of Data Storage Management" (Prentice Hall), author Jon William Toigo describes the holy grail as rational storage management. Toigo gives an overview of trends and technologies in the storage industry and points out the importance of storage virtualization. Although most storage analysts consider storage virtualization to be important, it's not a new concept. Most definitions of storage virtualization involve abstracting physical disks into a "pool" to present to a host as a logical, manageable object. Software alone, such as VERITAS's Volume Manager, or hardware and software combined, such as Compaq's forthcoming VersaStor Technology, can perform virtualization.
Storage virtualization is important to the storage industry, particularly to Windows 2000 and Windows NT administrators. Being able to pool disks and meter out storage capacity as volumes demand lets administrators greatly increase the amount of storage that they can manage more easily. Using storage virtualization blurs the advantages that a large enterprise-class storage server has over its small counterpart and the much greater advantages that both large and small servers have over Direct Attached Storage (DAS). Microsoft Windows 2000 is still a DAS world—but that's changing. Storage virtualization has a strong total cost of ownership (TCO) argument associated with it, and it's at the heart of Return on Investment (ROI) calculations that enterprise-class storage vendors show their customers.
If virtualization is the holy grail of storage, then many industry crusaders haven't yet reached it. Because you can use different elements of the I/O stack to think about physical disks abstractly, virtualization is a complex topic. Nearly every level of an OS's architecture offers some possibility for abstraction. At the network level, you can use a network service that acts as middleware to redirect calls to storage: DataCore SANsymphony takes this approach in an NT server; Vicom VIDR takes it on NT, AIX, Hewlett-Packard (HP)-UX, and Solaris; and FalconStor IPStor takes it on a Linux server. The advantage of using a network service is that it lets you combine storage from different storage vendors (at least in principle).
Virtualization is a major goal of Storage Area Networks (SANs), and the cost of SANs helps pay for the expensive testing and development work that storage virtualization technology requires. In many ways, Compaq's VersaStor is something of a wildcard—it's a standing joke in the industry that VersaStor has been "6 months away" from making the announcement for 2 or 3 years. The industry said the same about Win2K. However, Compaq demonstrated VersaStor's storage virtualization technology at Compaq's interoperability labs in Colorado Springs, where you can watch streaming video that shows data moving on-the-fly from one RAID set to another—another implication of virtualization: higher reliability and greater uptime. Expect to see VersaStor-enabled host bus adapters (HBAs) from several Compaq suppliers at announcement time.
XIOtech's Magnitude server is another example of how storage virtualization can be a powerful ally. XIOtech, which Seagate recently acquired, has built virtualization directly into its storage server at the disk level. A Magnitude server can pool a system's entire disk capacity to stripe across all disks. Unlike many volume managers, the Magnitude server can use any size disk completely, and it doesn't require that you create RAID volumes from identical subdisks. You can then use XIOtech's REDI management software to create all of the important RAID levels by using their disk stripes, which creates redundancy at the hardware level.
The Magnitude storage server supports all important hosts; it's easy to assign hosts to volumes. The server pools Magnitude's storage as a block device to present storage capacity to the Windows Disk Manager. You can quickly dole out space on an as-needed basis. The Magnitude server played a central role as a volume provider for four or five of the technology demonstrations at the Storage Networking Industry Association's (SNIA's) Storage Networking World 2000, proving its interoperability with most developing technologies. The ability to create volumes in seconds at the desired capacity for a wide variety of connections sets XIOtech apart from many storage server vendors at the present. A prominent financial analyst who follows storage industry acquisitions described Magnitude as "a superb midrange storage solution."
Most vendors involved in storage virtualization are also prominent members of the SNIA standards committees that are developing protocols for this new technology. You'll find most of the vendors I've mentioned, plus several more, at the next Storage Networking World in Orlando, Florida, in October. Storage virtualization is certainly an area worth paying attention to, one in which the industry is doing important work and releasing new products.