As much as the public cloud has started to work its way into the fabric of many enterprise computing infrastructures, a wide array of workloads still can't be moved into the cloud. Chief among them are those that center around specific performance requirements, security implications (especially in regulated industries), and getting a hold of and paying for high-speed network access to the cloud. However, even in these cases, it's highly desirable for business units to self-manage their computing resources and pay only for the resources they use.
In these situations, the construction of a private cloud can often satisfy many of the goals of going to the public cloud, while at the same time allowing the enterprise to implement whatever degree of performance capability and security infrastructure it requires. Likewise, maintaining infrastructure on premises removes the need to source potentially expensive WAN connections to the cloud.
Although building a private cloud shares many of the same steps as building an enterprise data center infrastructure, it is different in three key ways.