Capacity on demand The right approach? Storage utility options HP on computons Offloading storage management

One of the hallmarks of the new data center is flexibility, moving away from the confines of dedicated, paid-for, but nearly always underutilized or unused, resources. When it comes to storage, that flexibility means tapping into capacity on an automated, on-demand, pay-as-you-go basis.

While enterprise users have long entered into creative licensing agreements with vendors to reduce their capital outlay for storage, these latest pay-as-you-go, or metered, plans are another breed altogether. For the first time, storage actually can be purchased as a utility.

Metered storage plans, introduced in the past year, have advantages over capacity-on-demand programs. Cost management is one, and easier capacity planning another.

With metered storage, a company buys software or a server that collects information on the storage capacity being consumed on the array. The software then automatically transmits this data to the vendor's financial services department for billing. In this model, storage arrays often come configured with the amount of capacity a company estimates it will need, plus extra idle capacity. A user can grab as little or as much capacity as needed and only pay for the amount used per instance.

With capacity-on-demand, users buy a storage array with the extra capacity, and access this capacity in pre-negotiated chunks of data. They pay for all this data whether they use it or not.

St. Vincent Hospital & Health Services, a healthcare provider in Indianapolis, is using metered storage for its StorageTek L700e tape library. "We are buying tape slots only as we need them because they are heinously expensive," says Rich Banta, senior enterprise systems engineer at the company.

Banta says he only pays for the 40% capacity on the tape library being used, while getting an additional 60% to draw from when he needs it. Turning on the latent tape slots is simply a matter of getting a license key from StorageTek, Banta says.

Like StorageTek, EMC, HP and Sun offer metered storage options. EMC's metered offering comes through its OpenScale automated billing feature, which was introduced in 1999 and revamped with automatic usage collection and billing last year. OpenScale is available on a range of EMC products - the high-end Symmetrix, midrange Clariion, Centera nearline storage and for Connectrix Fibre Channel switches, and with value-added software products including the Symmetrix Remote Data Facility and TimeFinder.