EMC Corp. is to formally announce a program aimed at taking the guesswork out of buying storage by enabling customers to pay only for the gigabytes of capacity used.

The OpenScale programme has been available to select customers since 1999. But now the service is generally available to users of EMC hardware such as Celerra, Symmetrix and Clariion and software such as TimeFinder and Symmetrix Remote Data Facility.

"We chose OpenScale because it gives us flexibility in our demand for storage," says Eric Eriksen, CTO for Deloitte Consulting in Philadelphia. "It lets us do storage-on-demand at our facility and takes some of the guessing out of our acquisition of storage. If a client needs a certain amount of disk, we can have it ready the next day or the day after." Eriksen has an EMC Symmetrix with 80 terabytes of storage.

EMC meters a customer's use of storage assets, Fibre Channel switch ports, network-attached storage (NAS) servers and storage software via an Online ControlCenter agent that communicates with a billing system.

EMC, as well as rivals such as HP and IBM, have offered assorted storage-on-demand programs over the years whereby customers can 'turn on' chunks of storage capacity and notify the vendor that they have done so. What is different about OpenScale is the automation of the process through the company's Online Control Center, analysts say.

"This is the first time a vendor has combined storage-on-demand with technology that can audit use," says Brian Babineau, an analyst with consulting firm Enterprise Storage Group Inc.

In Online ControlCenter, a server or workstation is placed at a customer location, which monitors usage and performance information. This server, called the Collector, polls storage devices for usage, gathers the information and feeds it to a data warehouse located at EMC and then transferred automatically to EMC Global Finance so invoices can be generated based on the usage pattern.

Pricing depends on the equipment being used.