EMC, of course, would have us believe that Centera is in a class all its own, specifically, Content Addressed Storage, or CAS. Unlike other inexpensive disk arrays such as NetApp's IDE-based NearStore, Centera is not being positioned as an online backup solution, or as a replacement for tape.

Rather, EMC is pointing Centera at "data and documents that have thus far resisted being captured digitally," (e.g., archived paper documents such as cancelled checks) says John Webster, senior analyst and founder of the Data Mobility Group.

But according to Tom Hickman, senior product manager at EMC partner Connected Corp., a workstation backup service provider, Connected purchased Centera to replace the StorageTek libraries currently used to store customer backups.

Still, StorageTek doesn't appear particularly threatened. "We're very comfortable that the cost per megabyte for tape...

Besides, as Rick Gillette, founder and CTO of Storigen Systems in Lowell, MA, another EMC Centera partner, put it, "there will always be too much information to store on disk."

Case in point, the capacity of StorageTek's recently announced L5500 library - an open systems equivalent of the company's mainframe PowderHorn library - positively dwarfs Centera, with a mind-boggling 13PB of capacity.

EMC's traditional competitors, meanwhile, object to Centera's proprietary nature. To store data in Centera, an ISV must write to its API.

And far from trying to unify storage, complains Mark Lewis, vice president and general manager of Compaq's enterprise storage group, EMC is creating "another category of storage, another silo, another set of partner relationships."

"The API is a double-edged sword," says Forrester Research analyst Galen Shrek. On the one hand, "it enables a single object store," on the other - "it doesn't work with just anything." Regardless, he says, it's "pretty darn innovative."