Remotely accessible cloud storage isn't appropriate for all data types, but it's poised to attract a large amount of IT spending over the next few years.

That was the prediction Monday from Patrick Harr, founder and CEO of online storage vendor Nirvanix, one of several speakers at Storage Networking World to address the emerging cloud storage market.

"You will see a spending shift from what I call the traditional box model to more of an on-demand service model going forward," Harr told attendees at the conference in Dallas. (HP, OnStor and FalconStor are among vendors unveiling products  at Storage Networking World.)

When Harr began raising money for Nirvanix, the notion of the "cloud" was barely talked about, he said. Nirvanix didn't even mention the word "cloud" when it came out of stealth mode with a press release in September 2007. Although Nirvanix now uses the word to market its online storage service, Harr said the buzzword's ubiquity makes it difficult to cut through the hype and figure out exactly what cloud storage is and is not.

Cloud storage is not suitable for all data types, he noted, because it introduces some latency. "Every data has a storage type," Harr said. "Cloud storage is not meant to replace [storage-area network] storage." (Compare storage products.)

Simply making storage available over the Web does not make it a cloud service, he said. The analyst firm Gartner has defined cloud computing as "a style of computing where massively scalable IT-related capabilities are provided 'as a service' using Internet technologies to multiple external customers."

Cloud storage, Harr said, should be scalable from gigabytes to exabytes while using a single global namespace; load balancing will allow resources to be shifted to different geographic locations based on demand. Cloud storage should also be easy to connect to through Web services APIs or standard storage protocols; feature a fully redundant infrastructure; and be 80% to 90% less expensive than building one's own storage, he said.

Nirvanix offers cloud storage over the Web through its Storage Delivery Network, which is similar to Amazon's S3 storage service. Nirvanix on Monday announced general availability for a storage software offering called CloudNAS, an add-on to the Storage Delivery Network that lets users connect systems to Internet-based storage nodes via NFS, CIFS or FTP.