Mon, August 25, 2008 — Network World — If you're an IT executive, chances are you're already thinking about storage virtualization. Nearly one-quarter of companies with at least 500 employees have deployed storage virtualization products already, and another 55% plan to do so within two years, a recent Gartner survey found.

Storage virtualization is an abstraction that presents servers and applications a view of storage that is different from that of actual physical storage, typically by aggregating multiple storage devices and allowing them to be managed in one administrative console. (Compare storage virtualization products.)

The technology is emerging fast onto the enterprise scene for good reasons: In many cases, it can reduce the management burdens associated with storage; and offer better models for data-center migrations, backup and disaster recovery.

Enterasys Networks reaped these benefits recently when it moved a data center from Boston into its headquarters in Andover, Mass.

"In days gone by, before storage virtualization, that might have been an all-day, if not an all-week kind of process," says Enterasys vice president of marketing Trent Waterhouse. "Because of the storage virtualization technologies, the entire move happened in less than 30 minutes."

There are still common pitfalls that storage administrators should ponder, as well as questions they should ask before they roll out a storage-virtualization project. Here's a look at some of the top issues.

Managing capacity

With storage virtualization, allocating storage is easy -- perhaps too easy.

"You have the ability to affect more systems in the whole forest if you do something," says Jonathan Smith, CEO of ITonCommand in Denver, Colo., who cautions fellow IT shops to pay close attention to both the storage and performance needs of each application. "You just didn't have that power before. Now all of a sudden you can do whatever you want."

Smith, who is using LeftHand Networks virtualization on HP storage, says an IT pro might see a lot of empty space in a given storage volume and be tempted to fill it up. Overusing a resource, however, can decrease performance if the storage is allocated to a database or some other I/O-intensive application. (Compare storage products.)

"Make sure you size it correctly and really understand how much horsepower [your applications need]," Smith says.

These concerns are especially true when it comes to thin provisioning, a component of virtualization technology that lets an IT administrator present an application with more storage capacity than is physically allocated to it. This eliminates the problem of storage over-provisioning, in which storage capacity is pre-allocated to applications but never used.