Honestly, do you really know what storage virtualization is?


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One of the most confusing topics in IT today is storage virtualization. Even though the concept has been around for years in forms such as virtual memory in operating systems, virtual reality, tape virtualization and virtualization using logical volume managers, users continue to be perplexed by the many vendor announcements of "new" virtualization products. At the root of the confusion is the fact that vendors have defined the concept of virtualization in different ways to sell their own products, and then hyped the concept with religious fervor.

"In the last year or so, virtualization has been the most abused and misunderstood word in the computer field," says Thomas Brosnan, director of data center planning at Convergys, a Lake Mary, FL-based billing and customer care company. Brosnan has been using virtualization for several years to manage Convergys' 278TB of storage.

The confusion is compounded by vendors who proclaim that their virtualization solutions are "true virtualization," in the same way that resaligious zealots refer to their god as the only "true god," implying that other peoples' gods are "false gods." In addition to these religious wars, some vendors represent their virtualization solution as a new, free-standing technology instead of what it really is: an enabling technology for the management of heterogeneous storage environments. No wonder there's a cynical attitude toward virtualization (see "

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Virtualization has a credibility problem").

One reason that virtualization has become such a confusing term is because the software can be deployed in numerous places. For example, virtualization software can reside in the host in direct-attached storage, or several places in the storage area network (SAN): the host server, the storage array, on appliances (PC-like devices) that can be located in the data path - in which case they are called in-band or symmetrical - or outside of the data path - in which case they are called out-of-band or asymmetrical - or in intelligent switches.

Obviously, each vendor says its approach is best. Nick Allen, vice president of storage research at Gartner, a Stamford, CT-based consultancy disagrees. "There is not a best way to do virtualization," he says.

Host-based virtualization
Host-based virtualization, as implemented through logical volume managers, has been around for more than ten years. Veritas Software Corp., Mountain View, CA, introduced its Volume Manager 13 years ago. The Volume Manager software can be implemented on a single host, or in a cluster, in a Unix, or a Windows environment. In both cases, the Volume Manager gives users the ability to virtualize multiple storage arrays - that is, permitting users to aggregate logically into a pool made up of several physical disks.

Veritas' Volume Manager can be used in direct-attached configurations and in SANs. It permits online reconfiguration. For example, a storage manager can move from direct-attached storage to a SAN during production, without disrupting end users.

In addition to Volume Manager for virtualization, Veritas has a broad line of storage management applications and a file system, (VxFS) and has implemented many of these solutions so that the Volume Manager becomes an enabler, permitting storage management in a heterogeneous environment. And the fact that the Veritas' virtualization solution is software-only means that it can be deployed on a variety of storage devices including switches, storage routers, storage arrays and appliances - both in-band and out-of-band - providing block-level and file-level virtualization.

Michael Wojtowicz, manager of systems engineering at Entertainment Partners, a global service company located in Los Angeles, CA, which provides employment compensation and production services to the entertainment industry, has been using Veritas' virtualization software since 1996. When Wojtowicz moved from direct-attached storage in November 2001, the virtualization software saved the day.

"Without Veritas' virtualization software, we would never have been able to install the SAN while production was in progress without our users being aware that the change was being made," he says.

The storage array approach
EMC Corp., Hopkinton, MA, is a leading supplier of virtualization solutions implemented in the storage array. The company maintains that this approach is still one of the best means of implementing virtualization, according to Chuck Hollis, vice president of product marketing.

This was first published in June 2002

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