When you mention storage virtualization, people often think of pooling SAN storage across disk arrays from competing vendors, but that's not how storage virtualization is used in the real world.
According to Stephen Foskett, director of data practice for storage consulting services provider Contoural, storage virtualization includes volume management, path management software, thin provisioning and even data deduplication, as well as the traditional virtualization areas of pooling data on SAN or NAS devices.
"I tell people, even though you don't think you're using virtualization, you are. Even though you think you don't need it, you do," Foskett said. "You're using it already, you're going to be using it in the future. You just have to figure out what you're going to do with it."
Winter of 2004 was a busy time for storage virtualization. IBM's network-based SAN Volume Controller (SVC) was starting to pick up speed at around the time that Hitachi Data Systems launched its TagmaStore system with array-based virtualization, and EMC began banging the drums for its Invista switch-based virtualization. The idea of creating heterogeneous pools of storage was the driving factor for the introduction of all these products.
However, the concept of doing storage virtualization that way still hasn't been widely adopted. Even though IBM claims it has more than 4,000 SVC customers, Chris Saul, SVC marketing manager, says heterogeneous storage pooling is just picking up now. It's hard to say how many HDS customers are using heterogeneous storage arrays because the capability is in all of its systems. EMC hasn't sold much of Invista, although pronouncing it "ready for production" last December when version 2.0 rolled out. Its one reference customer, Purdue University, used Invista to migrate data from an older Symmetrix array to a newer one.
Block virtualization products continue to evolve. IBM recently chose SVC as its first product to incorporate thin provisioning, which it calls Space-Efficient Virtual Disks. More customers are using [SVC] for setting up tiers of storage using arrays from different vendors, Saul says. "In the past, people talked about [doing] that but it seemed like more trouble than it was worth."
Virtualizing storage is hardly top priority for many shops. In a survey of more than 760 companies conducted this spring by Storage magazine and SearchStorage.com, most of the respondents said they have virtualized some of their storage, but only around 25% said they would evaluate any type of storage virtualization in 2008.
"A lot of firms are still reluctant to go there because you're adding a layer of abstraction and complexity," says analyst Bob Laliberte, Enterprise Strategy Group. "They're taking a wait-and-see approach and making sure the technology is rock-solid.
People are still looking for the killer app that virtualization needs in order for it to take off, Foskett says. If heterogeneous arrays aren't that killer app, there are two other prime candidates: managing storage behind server virtualization and file management.
According to Laliberte, server virtualization has been driving adoption of networked storage because it's difficult to manage the data on all those virtual servers on DAS. Many shops turn to storage virtualization as the next step after they virtualize their servers.
"A lot of companies doing server virtualization are starting to do storage virtualization, and I expect we'll start seeing more storage virtualization being tied to server virtualization," Laliberte says. "With server virtualization, storage goes from servers to the SAN so server virtualization is driving the need for more storage management. People want to make those golden images and provision faster. A nonvirtualized array doesn't have enough storage so you need to go to a different one and that becomes a bottleneck. If you have a pool of storage you can provision to, it makes it go faster." NAS users went through a similar process a few years back as NAS filers began to proliferate and there was no way to manage files across NAS heads natively. "What people think of when they say virtualization is block virtualization on a Fibre Channel network," Foskett said. "But NAS virtualization is probably where the most mature and widest variety of virtualization products are."