Virtualization Basics and Fundamentals

A hypervisor is a software that enables a server to be logically abstracted and appear to the operating systems running on it as if they are running directly on the hardware itself. Vmware is the pioneer in virtualization technology and it defines Hypervisor as below

_{A hypervisor, also known as a virtual machine monitor, is a process that creates and runs virtual machines (VMs). A hypervisor allows one host computer to support multiple guest VMs by virtually sharing its resources, like memory and processing.}

The underlying operating systems sees the hypervisor as the actual computer. With virtualization, many operating systems can now run on a single server hardware platform, whereas in the past each operating system required its own physical server platform.

This is the core piece of technology which is used by the Cloud service providers to virtualize the infrastructure in a datacenter to offer compute, storage, network etc as a services. 

Types of Hypervisors

There are different types of Hypervisors available and each type has its own use cases.

Type1  Hypervisor

• The Type 1 hypervisor is installed and runs directly on top of the server hardware platform. This type is referred to as either bare-metal or native hypervisors.

• Type 1 hypervisors are generally more advanced and offer more features than a Type 2 and are found in the cloud datacenters as well as in the enterprise datacenters.

• Because the Type 1 hypervisor is running directly on top of the bare-metal hardware and not as an application on another operating system, it offers much higher performance, less overhead, and more security than a Type 2 hypervisor.

Type 2 Hypervisor

• The Type 2 hypervisor is installed as an application on an already existing operating system and allows to install the VMs in the application.

• For example, a PC running Windows can install a Type 2 hypervisor and run it as any other application. Then, inside the hypervisor, multiple operating systems or VMs can be run.  VMware workstation and VirtualBox from Oracle are examples of Type 2 hypervisors.

• Type 2 hypervisors are good for testing applications and in situations where dedicating a server to be virtualized is not desirable.

• This type of hypervisor does not offer the higher performance of a Type 1 since the Type 2 has the additional overhead of running on top of another operating system such as Windows or Linux and not directly on top of the bare-metal server hardware.

Also Read: Server and Application Virtualization Overview

Proprietary vs Opensource Hypervisors

• Hypervisors can be proprietary, they were developed and sold by private corporations such as Microsoft or VMware.

• Examples of proprietary hypervisors are Hyper-V developed by Microsoft and ESXi from VMware.

• Open source hypervisors are free for use by the public. Open source software is in the public domain, and there are no licensing fees.

• Some examples of fully functional open source hypervisors are KVM by Red Hat, VirtualBox from Oracle, and XenServer by Citrix.

• They provide complete virtualization of systems that allow for one or more VMs to run on the same server hardware platforms as the proprietary hypervisors.

Advantages and Disadvantages

• There are advantages and disadvantages to each approach. Generally proprietary hypervisors are fully supported by the vendor’s support agreements and have regular updates to add features and bug fixes.

• With open source, support is generally offered in community forums, with a few companies offering support agreements.