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Oracle® VM User's Guide
Release 3.0 for x86

Part Number E18549-03
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1 Introduction to Virtualization

This chapter provides introductory information on virtualization. It discusses why you would want to use virtualization, the technology provided, and a high level overview of Oracle VM. It contains the following sections:

1.1 Introduction to Virtualization

The IT industry's focus on virtualization technology has increased considerably in the past few years. However, the concept has been around much longer, as you can read in the brief history below. This section also provides a high level view of the virtualization technology and methods that exist today, and highlights a number of reasons why organizations are embracing virtualization more and more.

1.1.1 Brief History of Virtualization

The concept of virtualization is generally believed to have its origins in the mainframe days in the late 1960s and early 1970s, when IBM invested a lot of time and effort in developing robust time-sharing solutions. Time-sharing refers to the shared usage of computer resources among a large group of users, aiming to increase the efficiency of both the users and the expensive computer resources they share. This model represented a major breakthrough in computer technology: the cost of providing computing capability dropped considerably and it became possible for organizations, and even individuals, to use a computer without actually owning one. Similar reasons are driving virtualization for industry standard computing today: the capacity in a single server is so large that it is almost impossible for most workloads to effectively use it. The best way to improve resource utilization, and at the same time simplify data center management, is through virtualization.

Data centers today use virtualization techniques to make abstraction of the physical hardware, create large aggregated pools of logical resources consisting of CPUs, memory, disks, file storage, applications, networking, and offer those resources to users or customers in the form of agile, scalable, consolidated virtual machines. Even though the technology and use cases have evolved, the core meaning of virtualization remains the same: to enable a computing environment to run multiple independent systems at the same time.

1.1.2 Hypervisor

If virtualization is defined as enabling multiple operating systems to run on a single host computer, then the essential component in the virtualization stack is the hypervisor. This hypervisor, also called Virtual Machine Monitor (VMM), creates a virtual platform on the host computer, on top of which multiple guest operating systems are executed and monitored. This way, multiple operating systems, which are either multiple instances of the same operating system, or different operating systems, can share the hardware resources offered by the host.

Hypervisors are commonly classified as one of these two types, as show in Table 1-1, "Hypervisor Types".

Table 1-1 Hypervisor Types

Classification Characteristics and Description

Type 1: native or bare metal

Native hypervisors are software systems that run directly on the host's hardware to control the hardware, and to monitor the guest operating systems. Consequently, the guest operating system runs on a separate level above the hypervisor. Examples of this classic implementation of virtual machine architecture are Oracle VM, Microsoft Hyper-V, VMWare ESX and Xen.

Type 2: hosted

Hosted hypervisors are designed to run within a traditional operating system. In other words, a hosted hypervisor adds a distinct software layer on top of the host operating system, and the guest operating system becomes a third software level above the hardware. A well-known example of a hosted hypervisor is Oracle VM VirtualBox. Others include VMWare Server and Workstation, Microsoft Virtual PC, KVM, QEMU and Parallels.

1.2 Reasons to Use Virtualization

There are many different good reasons for companies and organizations to invest in virtualization today, but it is probably safe to assume that financial motivation is number one on the list: virtualization can save a lot of money. Below is an overview of the key benefits of virtualization.

Table 1-2 Reasons to Use Virtualization

Item Description

Resource optimization

Today's enterprise level computer resources are so powerful that they often have excess capacity. By virtualizing the hardware and allocating parts of it based on the real needs of users and applications, the available computing power, storage space and network bandwidth can be used much more effectively. Computers no longer need to be idle or performing below their capabilities because there are fewer connected users, or because the hosted application happens to be less demanding than the server can handle.

Virtual machines offer software developers isolated, constrained, test environments. Rather than purchasing dedicated physical hardware, virtual machines can be created on the existing hardware. Because each virtual machine is independent and isolated from all the other servers, programmers can run software without having to worry about affecting other applications, or external components affecting the execution of their code.


It is common practice to dedicate individual computers to a single application. If several applications only use a small amount of processing power, the administrator can consolidate several computers into one server running multiple virtual environments. For organizations that own hundreds or thousands of servers, consolidation can dramatically reduce the need for floor space, HVAC, A/C power, and co-location resources. This means the cost of ownership is reduced significantly, since less physical servers and floor and rack space are required, which in turn leads to less heat and power consumption, and ultimately a smaller carbon footprint.

Maximizing Uptime

Agility is all about being able to respond to changing requirements as quickly and flexibly as possible. Virtualization brings new opportunities to data center administration, allowing users to enjoy:

  • Guaranteed uptime of servers and applications; speedy disaster recovery if large scale failures do occur.

  • Instant deployment of new virtual machines or even aggregated pools of virtual machines via template images.

  • Elasticity, that is, resource provisioning when and where required instead of keeping the entire data center in an always-on state.

  • Reconfiguration of running computing environments without impacting the users.

Automatically Protect Applications from Server Failure

Server virtualization provides a way to implement redundancy without purchasing additional hardware. Redundancy, in the sense of running the same application on multiple servers, is a safety measure: if for any reason a server fails, another server running the same application takes over, thereby minimizing the interruption in service. This kind of redundancy works in two ways when applied to virtual machines:

  • If one virtual system fails, another virtual system takes over.

  • By running the redundant virtual machines on separate physical hardware you can also provide better protection against physical hardware failure.

Easily Migrate Workloads as Needs Change

Migration refers to moving a server environment from one place to another. With most virtualization solutions it is possible to move a virtual machine from one physical machine in the environment to another. With physical servers this was originally possible only if both physical machines ran on the same hardware, operating system and processor. In the virtual world, a server can be migrated between physical hosts with entirely different hardware configurations. Migration is typically used to improve reliability and availability: in case of hardware failure the guest system can be moved to a healthy server with limited downtime, if any. It is also useful if a virtual machine needs to scale beyond the physical capabilities of the current host and must be relocated to physical hardware with better performance.

Protect Investment in Existing, Legacy Systems

Server hardware will eventually become obsolete, and switching from one system to another can be difficult. In order to continue offering the services provided by these legacy systems, you can run it as a virtual machine on new, modern hardware, while the legacy system itself still behaves as if it were running on the same legacy hardware. From an application perspective, nothing has changed. In fact, its performance may well benefit from the newer underlying hardware. This gives the organization the time to transition to new processes without worrying about hardware issues, particularly in situations where the manufacturer of the legacy hardware no longer exists or cannot fix broken equipment.

1.3 Xen™ Technology

Oracle VM is built upon Xen technology, using the Xen hypervisor. The Xen hypervisor is a small, lightweight bare metal hypervisor for x86-compatible computers. The Xen hypervisor securely executes multiple virtual machines on one host computer. Each virtual machine has its own guest operating system with almost native performance. The Xen hypervisor was originally created by researchers at Cambridge University, and derived from work done on the Linux kernel.

Oracle VM insulates users and administrators from the underlying virtualization technology and allows daily operations to be conducted using goal-oriented GUI interfaces.

1.4 Oracle VM for x86

Oracle VM for x86 (Oracle VM) is a platform that provides a fully equipped environment with all the latest benefits of virtualization technology. Oracle VM enables you to deploy operating systems and application software within a supported virtualization environment. The components of Oracle VM are:

Figure 1-1, "Oracle VM Architecture" shows the components of Oracle VM.

Figure 1-1 Oracle VM Architecture

Description of Figure 1-1 follows
Description of "Figure 1-1 Oracle VM Architecture"

Oracle VM Manager is an Oracle WebLogic Server application running on Oracle Linux. This can be a standalone computer, or part of a virtual machine running on an instance of Oracle VM Server.

Oracle VM Server is installed on a bare metal computer, and contains the Oracle VM Agent to manage communication with Oracle VM Manager. Dom0 is an abbreviation for domain zero, the management domain with privileged access to the hardware and device drivers. DomU is an unprivileged domain with no direct access to the hardware or device drivers. A user-domain (domU) is started and managed on an Oracle VM Server by dom0.

1.4.1 Oracle VM Integrated Support

Oracle has a unique position in the virtualization market as an Enterprise application, operating system and hardware vendor that delivers technologies across the stack. Owning the entire stack has various advantages:

  • integration and centralized management of all components

  • the ability to pre-package and distribute Oracle technologies via Oracle VM templates

  • integrated enterprise support across the entire technology stack, from application to hardware

Oracle VM support is an add-on component of Oracle's enterprise support package that offers an end-to-end single vendor support solution from the application to the disk. A single support call covers the entire Oracle stack which expedites problem resolution. Using Oracle support allows an Oracle support service request (SR) to transition between support teams with issues that require cross stack collaboration. For example, if you open a service request for an application issue and the root cause is at the virtualization layer then the service request will transition between the application and virtualization teams.