As senior director of enterprise technology operations at Corrections Corporation of America (CCA), a prison management firm that handles more than 60 facilities, Brad Wood faces several challenges. His group manages approximately 100TB of data -- including inmate medical records, operational records, e-mail, and so forth -- across four Hitachi Data Systems (HDS) storage arrays in two datacentres. Because of federal and state rules, much of the company's data is mirrored three or four times to keep it accessible in case of failure. Adding to the complexity, Wood buys his hardware based on current price and performance, so he has a mix of suppliers.

With costs escalating, Wood needed a way to slow deployment of new storage hardware and make better use of the disparate hardware he already had. The solution he chose was to implement storage virtualization.

The idea behind virtualization sounds deceptively simple. It aggregates storage systems (such as arrays) from multiple providers into a networked environment that can be managed as a single pool. In essence, "the storage controller is being disaggregated and spread around the network," says Brian Garrett, lab technical director at Enterprise Strategy Group (ESG), a market research firm.

In Wood's case, his storage engineer can now manage the company's various hardware from a single console, using Symantec Veritas Storage Foundation and HDS HiCommand software.

Storage virtualization has several key IT benefits in addition to improved resource utilization. For one, it allows data to be moved to any storage device in the pool when subsystems fail or are replaced. Easier data migration also makes it possible to implement a tiered storage architecture cost-effectively, one in which data is moved to less expensive, lower performance systems as it becomes less business-critical over time.

Another benefit is easier replication, because virtualization removes the need for full redundancy. Without storage virtualization, IT typically must copy entire volumes from one storage type to another in order to ensure all related data is in one environment. With virtualization, it's easier to copy partial data -- such as snapshots or delta files -- and keep it linked to the entire data set across physical devices.

And, of course, maintenance costs are always a factor. "[Virtualization] also reduces the storage administration burden over time by getting storage folks out of the server business," notes Rick Villars, IDC vice president of storage systems research.

If you listen to storage vendors, every product offers some form of virtualization. Since 2000, the term has been hyped consistently. Although skepticism is warranted, storage virtualization is now real enough that enterprises can begin at least exploring its use as an enabling technology to simplify storage management in heterogeneous environments. Many enterprises, like CCA, have found they can get real benefits today.

Three Approaches to Virtualization

Vendors offer three approaches to true storage virtualization: host-client (via software), in-fabric (mainly through appliances but soon also through switches), and in-array (embedded functionality). While the vendors tout specific pros and cons of each approach (see the infographic on page 39), analysts agree that they all deliver in the end. The determining factor is usually how well a particular approach fits into your existing storage infrastructure, says Gartner research director Stan Zaffos.

The in-fabric approach is the most common method, offered in products such as DataCore Software's SANsymphony, EMC's InVista, FalconStor's IPStor, IBM's SVC (SAN Volume Controller), NetApp's V-Series, and StoreAge's SVM. These products, which have been on the market for just a few years, use dedicated appliances or software running on a server to discover storage resources and then build the metadata that lets IT manage them as a virtual pool. Of these, IBM and NetApp have the largest installed bases (about 1,000 each), Zaffos notes.