If you've read about virtualization, you've bumped into the term hypervisor. You may have found this word to be a little scary. (We did when we first read it.) The concept isn't technically complicated, however.

The beauty of this arrangement is that the hypervisor does all the heavy lifting. The guest OS doesn't have any idea that it's running in a virtual partition; it thinks that it has a computer all to itself.

One of the benefits of virtualization is the way that it abstracts hardware assets, in essence allowing a single piece of hardware to be used for multiple tasks.

The following list summarizes hardware abstraction and its management:

Managing a virtual environment involves some foundational issues that determine how well the components function as a system. These issues include how licenses are managed, how workloads are controlled, and how the network itself is managed. The reality is that IT sits between the network's static virtualization and the dream of full automation. We discuss some foundational issues in the following sections.

Managing virtualization requires an abstraction layer that hides and manages things between the physical storage subsystems. The virtualization software needs to be able to present the whole storage resource to the virtualized environment as a unified, sharable resource. That process can be more difficult than it sounds. All the administrative functions that you'd need in a physical data center have to be deployed in a virtualized environment, for example. Following are some of the most important considerations:

Provisioning software enables the manual adjustment of the virtualized environment. Using provisioning software, you can create new virtual machines and modify existing ones to add or reduce resources. This type of provisioning is essential to managing workloads and to moving applications and services from one physical environment to another.

Provisioning software enables management to prioritize actions based on a company's key performance indicators. It enables the following:

Increasingly, organizations also need to virtualize storage. This trend currently works in favor of NASes rather than SANs, because a NAS is less expensive and more flexible than a SAN.

In addition to application data, virtual machine images need to be stored. When virtual machines aren't in use, they're stored as disk files that can be instantiated at a moment's notice. Consequently, you need a way to store virtual-machine images centrally.

Before virtualization, hardware provisioning was simply a matter of commissioning new hardware and configuring it to run new applications or possibly repurposing hardware to run some new application.

Virtualization makes this process a little simpler in one way: You don't have to link the setup of new hardware to the instantiation of a new application. Now you can add a server to the pool and enable it to run virtual machines. Thereafter, those virtual machines are ready as they're needed. When you add a new application, you simply configure it to run on a virtual machine.

The hypervisor (refer to "Using a hypervisor in virtualization," earlier in this chapter) lets a physical server run many virtual machines at the same time. In a sense, one server does the work of maybe ten. That arrangement is a neat one, but you may not be able to shift those kinds of workloads without consequences. A server running 20 virtual machines, for example, may still have the same network connection with the same traffic limitation, which could act as a bottleneck. Alternatively, if all those applications use local disks, many of them may need to use a SAN or NAS — and that requirement may have performance implications.

Based on this background, we define cloud computing as a computing model that makes IT resources such as servers, storage, middleware, and business applications available as a service to business organizations in a self-service manner. Although all these terms are important, the important one is self-service.

When you bring these elements together, you have something very powerful.

What type of cloud services will customers subscribe to? All the services that we describe as the foundation of virtualization (refer to "Understanding Virtualization," earlier in this chapter) are the same ones that you'd make available as part of the cloud. You want to be able to access CPU cycles, storage, networks, and applications, for example, or you may want to augment the physical environment with additional CPU cycles during a peak load. Alternatively, you may want to replace an entire data center with a virtualized data center that's based on a virtualized environment managed by a third-party company.

Cloud computing is in its very early stages. In fact, in many situations customers aren't even aware that they're using a cloud. Anyone who uses Google's Gmail service, for example, is leveraging a cloud, because Google's own search environment runs within its own cloud. In other situations, large corporations are experimenting with cloud computing as a potential way to transfer data center operations to a more flexible model.

Another example is Amazon.com, which sells access to CPU cycles and storage as a service of its cloud infrastructure. A customer may decide to use Amazon's cloud to test a brand-new application before purchasing it, because renting is easier than owning.

In cloud environments, customers add CPU cycles or storage as their needs grow. They're protected from the details, but this protection doesn't happen by magic. The provider has to do a lot of work behind the scenes to manage this highly dynamic environment.

For decades, thinkers have talked about the day when we would move to utility computing as a normal model of managing computing resources. Computing power would be no different from electricity. When you need some extra light in a room, for example, you turn on the light switch, and the electric utility allocates more power to your house. You don't have an electrical grid in your home, and you don't have to acquire tools to tune the way that power is allocated to different rooms of your home. Like electrical power, computing power would be a highly managed utility.

Obviously, we're far from that scenario right now. The typical enterprise is filled with truly heterogeneous data centers, assorted servers, desktops, mobile devices, storage, networks, applications, and vast arrays of management infrastructures and tools. In fact, you may have been told that about 85 percent of these computing resources are underused.

In addition, at least 70 percent of the budget spent on IT keeps the current systems operational rather than focusing on customer service. The advent of cloud computing is changing all that. Organizations need to reduce risk; reduce costs; and improve overall service to their customers, suppliers, and partners. Most of all, they need to focus on the service levels of the primary transactions that define the business.

Any vendor that wants to provide cloud services to its customers has a lot to live up to. All the virtualization technology that supports these requirements is hidden from the customer. Although the customer may expect to run a wide variety of software services on the cloud, she may have little, if any, input into the underlying services.

Cloud customers see only the interface to the resources. In this self-service mode, they have the freedom to expand and contract their services at will. Vendors providing cloud services have to provide a sophisticated service-level agreement (SLA) layer between the business and the IT organization. The vendors have a responsibility to provide management services, including a service desk to handle problems and real-time visibility of usage metrics and expenditures. For two reasons, it's the vendor's responsibility to provide a completely reliable level of customer service:

Overseeing and managing a cloud environment are complicated jobs. The provider of the cloud service must have all the management capabilities that are used in any virtualized environment. In addition, the provider must be able to monitor current use and anticipate how it may change. Therefore, the cloud environment needs to be able to provide new resources to a customer in real time. Also, a high level of management must be built into the platform. Much of that management needs to be autonomic — self-managing and self-correcting.