Sorting out storage

Storage-area networks (SAN) are fast becoming part of the IT lexicon, but the abundance of other storage management acronyms is making things a bit confusing.

A SAN is a collection of networked storage devices that can automatically communicate with each other. It's important to note that a SAN doesn't have to use Fibre Channel as its underpinnings, according to Tom Lahive, senior storage systems analyst at market researcher Dataquest in San Jose. For example, the mainframe environment's Enterprise Systems Connection channels could form the SAN interface.

"The key to understanding what makes a SAN is understanding that the goal is to divorce all users and network administrators from storage management," Lahive says. "Storage, retrieval and file transfers are automatically managed in a true SAN."

OK, so what is network-attached storage (NAS)? SANs may include NAS-enabled devices, but they aren't the same thing.

A NAS system is connected to application servers via the network. But unlike a SAN, with NAS, users can directly access stored data without server intervention, Lahive says. A SAN will automate management of storage systems, while NAS devices don't have this capability.

And when it comes to automated management in a SAN, there's yet another definition floating around: hierarchical storage management (HSM). "HSM is simply managing data movement from online to offline storage, such as to tape devices," Lahive says.