Research firm IDC recently released a new study indicating that the total revenue for public and private cloud server deployment will hit $9.4 billion by 2015. The study breaks down that number by public cloud server deployment ($3.6 billion) and private cloud server deployment ($5.8 billion).

The study, Worldwide Enterprise Server Cloud Computing 2011-2015 Forecast, further forecasts that the number of servers shipped for deployment in public clouds will reach more than 1.2 million in 2015, representing a 2011 to 2015 compound annual growth rate (CAGR) of 21.1 percent. Meanwhile, more than 570,000 servers are projected to be shipped for deployment into private clouds in 2015, representing a five-year CAGR of 22.4 percent.

We talked with Katie Broderick, senior research analyst in IDC’s Enterprise Platforms and Datacenter Trends and Strategies group, about the study and the firm’s views on cloud industry evolution.

What did you find in this study that was most surprising to you?

One surprise was the rise in public cloud system prices. As public clouds try to become more “enterprise-ready,” that is changing the types of servers they’re buying.

What are some of the hurdles that still need to be addressed to accelerate enterprise cloud adoption?

The number one hurdle is security. The recent outages and breaches at Amazon and Sony are not instilling confidence in enterprise IT managers. They still see public cloud as a test and development/developer sandbox offering rather than a production/enterprise-ready environment.

Are those challenges being addressed sufficiently, in your view?

I think public cloud providers are working hard to ensure their datacenters and networks are secure. It is a tough job because a large reserve of data, like a public cloud, makes a large target.

Your study compares public cloud and private cloud. Both are viable options for different applications —but will one prevail, ultimately?

No. The solution for most enterprises in the end will be hybrid cloud (a mix of public and private cloud). Even today, most enterprises have some compute outsourced, hosted and some in-house. Where the compute goes will depend on the workload because each has a different compliance requirement, service-level and risk level.

Are there still applications that you think enterprises should keep off the cloud, no matter what—public or private?

No, I think it depends on the cloud setup. Any workload could go to public or private cloud—it just depends on if the IT organization is willing to withstand the corresponding risks and costs. There are some apps that the software vendor will not support in certain environments (virtualized, for example), but it is technically possible in many cases to virtualize anyway.