Should You Care About the Standard Definitions for Storage Virtualization?

If you've picked up a storage trade magazine or spoken to a storage networking-products vendor in the past 6 months, you know that virtualization is a hot topic. We hear its features and benefits bantered around—how virtualization will save money and solve all our management problems.

Although such talk sounds great, unfortunately most vendors are singing their own tune while three blocks away another vendor is saying exactly the same thing about a completely different technology. Consequently, companies that have real answers to business problems find that customers are putting them on hold as they try to cut through the confusion that surrounds this topic.

Virtualization is a relatively intuitive concept. You take something that's not real and make it seem as if it is. TechWeb, an online technical encyclopedia, defines storage virtualization this way: "Treating storage as a single logical entity without regard to the hierarchy of physical media that may be involved or that may change. It enables the applications to be written to a single programming interface rather than to the details of the various disk, tape, and optical devices that are used." In other words, virtualization provides the ability to deliver capacity to users and applications without requiring them to deal with traditional logical-to-physical mapping of LUNs to storage.

Because we can simplify the broad concept of storage virtualization to the degree that it's almost meaningless, understanding the specifics of what vendors mean when they talk about this technology is important. If you ask six IT administrators for a definition of virtualization, you'll likely get six different answers—each a description of an individual vendor's marketing spin on the company's particular product. Virtualization is evolving to address not only traditional Direct Attached Storage (DAS) environments, but the special architectures of Storage Area Network (SAN) and Network Attached Storage (NAS) as well. When one vendor talks about virtualization, is he or she really talking about traditional RAID technologies, or does the product that he or she is proposing add policy-based storage-management functionality? Is it Hierarchical Storage Management (HSM) or is it NAS aggregation? Does it provide in-band aggregation of file system data or out-of-band management of a storage pool?

The Storage Networking Industry Association (SNIA) has been working on standard definitions for the numerous terms associated with storage virtualization. In summary, SNIA has defined three areas within a storage system (storage, network and server components, and management software) in which virtualization can take place. These identified areas are host-based virtualization (e.g., logical volume managers, HSM software), storage-subsystem virtualization (e.g., RAID) and storage network virtualization (e.g., in-band or out-of-band virtualization appliances resident in the storage network). Along with these concepts, SNIA is defining individual terms for specific types of virtualization and virtualization services.

Why is defining individual terms for virtualization important, and why should a user care? As we've seen in the past, particularly in the buzzword-rich storage-networking industry, confusion rules when several vendors bring any new technology to market. Marketing often takes over when vendors release to the general public immature products that will add value over time. Six IT administrators will give six different definitions of virtualization because six different vendors have seized on the current allure of the word and are using it—and sometimes stretching it— to cash in on the current hype.

Standard definitions that a reputable group offers are critical to end users' understanding of new technology. Standard definitions give context to the functionality, features, and benefits that a particular vendor proposes. Even when the industry doesn't widely accept proposed standard definitions (usually because of the marketing strength of one or more large vendors), these definitions still help customers understand technology and help them determine the truth or fiction of the vendors' claims. Solid definitions for virtualization, in particular, are what end users need as they begin to consider how virtualization will help them use their storage in ways that are appropriate for each application.

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