Defining Virtualization

Virtualization separates resources and services from the underlying physical delivery environment. With its use, you can create many virtual systems within a single physical system. A primary driver for virtualization is consolidating servers, which provides organizations with efficiency and potential cost savings.

Characteristics

Virtualization has three characteristics that make it ideal for cloud computing:

check.png Partitioning: In virtualization, many applications and operating systems are supported in a single physical system by portioning (separating) the available resources.

check.png Isolation: Each virtual machine is isolated from its host physical system and other virtualized machines. Because of this isolation, if one virtual instance crashes, the other virtual machines aren’t affected. In addition, data isn’t shared between one virtual container and another.

check.png Encapsulation: A virtual machine can be represented (and even stored) as a single file, so you can identify it easily based on the services it provides. For example, the encapsulated process could be a business service. This encapsulated virtual machine could be presented to an application as a complete entity. Thus, encapsulation could protect each application so that it doesn’t interfere with another application.

tip.eps Here’s a nontechnical analogy to help you think about virtualization. Some experts have likened virtualization to an apartment building. Individual apartments share a building. They are each isolated, but they share utilities in a more efficient model than a house might.

In server virtualization, one physical server is partitioned into multiple virtual servers. For example, the hardware resources of a machine — including the random access memory (RAM), CPU, hard disk, and network controller — can be virtualized into a series of virtual machines that run their own applications and operating system on these machines. A thin layer of software is actually inserted onto the hardware that contains a virtual machine monitor or hypervisor, which is described in the next section.

Using a hypervisor in virtualization

System virtualization can be approached through hardware partitioning or hypervisor technology. Hardware partitioning subdivides a physical server into fractions, each of which can run an operating system. Although this model supports consolidation of hardware, according to experts, it doesn’t have the full benefits of resource sharing and emulation that hypervisors do.

A hypervisor allows multiple operating systems to share a single host. It knows how to act as a traffic cop to make things happen in an orderly manner. The hypervisor sits at the lowest levels of the hardware environment and uses a thin layer of code in software to enable dynamic resource sharing. The hypervisor makes it seem like each operating system has the resources all to itself.

A short history of virtualization

IBM introduced virtualization in the early 1960s to enable users to run more than one operating system on a mainframe. Mainframe virtualization became less relevant in the 1980s and 1990s. Indeed, in the 1990s, companies stopped worrying about the efficiency of the computer platform because computers were becoming so powerful.

For more than a decade, IT organizations expanded the capabilities of their data centers by adding servers. Servers had become so cheap that each time a new application was added, it was easier to buy a new server than to share resources with other applications. Eventually, organizations realized that maintaining, upgrading, and managing a large (and growing) number of servers was getting out of hand. The number of support-staff employees required to operate the data center was climbing swiftly, so the manpower cost of maintaining the data center (as a percentage of total cost) was rising. At the same time, other costs were growing in an unpredicted manner, particularly the costs of electricity (to power the computers), air conditioning (to cool them), and floor space (to house them).

One of the main problems was that the servers were horribly inefficient. In the days of the mainframe, great efforts were made to use 100 percent of the computer’s CPU and memory resources. Even under normal circumstances, it was possible to achieve a better than 95 percent utilization. On the cheap servers that IT departments had been deploying, however, CPU inefficiency was often 6 percent or less — sometimes as low as 2 percent. Memory and disk input/output (I/O) usage were similarly low.

This situation seems almost insane until you realize that many applications simply don’t require a great deal of resources, and with the servers that were being delivered by the year 2000, you didn’t put more than one application on a server. Why? Because the operating systems that almost everyone had — Windows and Linux, typically — couldn’t effectively schedule resource use between competing applications. In a competitive hardware market, vendors began increasing the power of the servers, at an affordable price. Most of these servers had more power than a typical application needed. If an organization decided to stay with older but lower-powered hardware, it couldn’t find people to maintain those aging platforms.

If you had an application that only ever needed 4 percent of a current CPU, what were you going to do other than provide it with its own server? Some companies actually used old PCs for some applications of this kind, maintaining the PCs for themselves; but there’s a limit to the amount of old equipment that you can reuse.

The solution to this squandering of resources was to add scheduling capability to computers, which is precisely what one IT vendor, VMware, introduced. Adding scheduling changed the dynamics of computer optimization and set the stage for the modern virtualization revolution. The mainframe is dead; long live the mainframe!

Because in cloud computing you need to support many different operating environments, the hypervisor becomes an ideal delivery mechanism. The hypervisor lets you show the same application on lots of systems without having to physically copy that application onto each system. One twist: Because of the hypervisor architecture, it can load any (or many) different operating system as though it were just another application. So, the hypervisor is a very practical way of getting things virtualized quickly and efficiently.

remember.eps You need to understand the nature of the hypervisor. It’s designed like a mainframe OS rather than like the Windows OS. The hypervisor, therefore, schedules the access that guest operating systems have, everything from the CPU, to memory, to disk I/O, to other I/O mechanisms. With virtualization technology, you can set up the hypervisor to split the physical computer’s resources. Resources can be split 50:50 or 80:20 between two guest operating systems, for example.

The beauty of this arrangement is that the hypervisor does all of the heavy lifting. The guest operating system doesn’t care (or have any idea) that it’s running in a virtual partition; it thinks it has a computer all to itself.

There are basically two types of hypervisors:

check.png Type 1 hypervisors run directly on the hardware platform. They achieve higher efficiency because they’re running directly on the platform.

check.png Type 2 hypervisors run on the host operating system. They are often used when there’s a need to support a broad range of I/O devices.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
18.118.7.102