Villars went on to project a compound annual growth rate of 28.9% for cloud storage from last year on to 2015. That would put worldwide expenditures at an amazing $11.7 billion.

To put this in perspective: Last June, IDC calculated worldwide expenses in 2010 for on-premise storage to have reached $30.8 billion. With a 3.9% CAGR, the firm's analysts expect expenses in that category to reach $37.3 billion by 2015. Unforeseen economic circumstances during this time period would probably impact corporate spending in both categories roughly equally. So the firm takeaway from this latest forecast is this: IDC projects the percentage of all enterprise storage spent on the public cloud to rise from 9.5% last year to almost 24% in 2015.

IDC gave RWW a taste of the contents of Villars report this afternoon. In it, he projects three driving trends:

1. First, enterprise storage hardware purchases will start to be driven by two relatively new packaging options, both of which concern private cloud architecture. Bundled storage with all-in-one "out-of-the-box solution" hardware, such as the database appliances we've seen announced by Oracle earlier this month and HP and Microsoft soon afterward, will take root in more data centers. And private cloud architectures such as OpenStack will give new data centers a new and more scalable storage nucleus. But in both cases, those storage pools are designed to be expandable through public cloud-based storage supplements, which will leave the back door unlocked for storage-on-demand.
2. "Storage software has traditionally formed the foundation for the management, protection, organization, and availability of storage capacity," IDC tells RWW. As more storage management software is revised to make public cloud-based options more readily available, businesses will naturally take a liking to them.
3. As businesses ponder the question of how they're going to cope with this explosion of data in the first place, they'll be bringing in professional services and consultants. They'll promise to take care of this for businesses, and they'll haul in the public cloud through the front gate. "Overall, the market for professional services aimed at enabling enterprises with private cloud storage is larger and growing faster than that of public cloud storage providers," says IDC, "although both represent a significant opportunity."

IDC's Villars also projected expenditures by service providers on public cloud storage will grow from $3.8 billion in 2010 to $10.9 billion in 2015, at a CAGR of 23.6%. So obviously IDC believes their margins will improve a bit as well.