What is virtualization?
As the name indicates, virtualization means creating virtual version of something and not real ones. Virtualization can be done on hardware, operating systems, storage devices and computer network resources.
What is Server Virtualization?
Server Virtualization can be defined as the masking of server resources. These resources will include number and identity of physical servers, processors, and operating systems from the server users. This server virtualization is achieved by using a software application by the server administrator. This software application divides the physical server into multiple isolated virtual environments.
Types of Server Virtualization
Virtual machines run on the physical server and their operating systems also can vary from virtual machine to virtual machine. The operating system of the virtual machine is called the guest operating system. All these guest operating systems are being run on the host operating system. Every virtual machine that runs in this manner is totally unaware of other software that is also running in the same fabric.
Now, we are going to see the various types of server virtualization. The various types of the server virtualization are listed below.
1) Guest OS/Virtual Machine Model
2) Hypervisor Model
3) Para Virtualization Model
4) Full Virtualization Model
5) Hardware Virtualization Model
6) Kernel Base Virtualization Model
7) Shared Kernel Virtualization Model
These are the various server virtualization techniques in use now. Let’s see each of them in detail.
Guest OS/Virtual Machine Model
The Guest OS/Virtual Machine Model is very common type virtualization. In this type, each virtual machine, usually called VM, runs as a separate instance of operating system within the virtualization software and the virtualization software runs in another operating system which is actually installed on the hardware. The operating system that runs the virtualization software runs is called the Host Operating system because it provides the environment for virtualization
The next type of the Virtualization is the Hypervisor Model. In this model, there is a thin layer of software called Hypervisor. It is otherwise called Virtual Machine Monitor (VMM). The VMM runs on the top of the hardware and provides the environment including necessary features and services required for smooth operation and execution of virtual machine. The hypervisor identifies traps and responds to protected or privileged CPU instructions made by each virtual machine. The hypervisor is responsible to handle queuing, dispatching, and execution of virtual machines.
Para Virtualization Model
This is also on the hypervisor virtual machine. It imitates trapping-and-emulation overhead with the software implemented virtualization. It requires the guest operating system to be recompiled or modified before installation on the virtual machine. It is done to ensure performance enhancement because the modified guest OS communicates directly with the hypervisor.
Full Virtualization Model
The Full Virtualization Model is very similar to the previous model which is Para Virtualization Model. It contains functionality to emulate the underlying hardware when necessary. The Full Virtualization causes the hypervisor to trap the machine operations the OS uses to read or modify the system’s status or perform the input and output operations. After it has trapped them, the hypervisor emulates these operations in software and returns status codes consistent with what the real hardware would deliver. It’s the reason for unmodified operating systems can run on the top of the hypervisor.
Hardware Virtualization Model
It is very similar to the Para virtualization model and the Full Virtualization Model in its operation. It uses a hypervisor technique but it is only available on systems that support hardware virtualization.
Kernel Base Virtualization Model
The Kernel Base Virtualization Model does not require a hypervisor, but instead runs a separate version of the Linux kernel and an associated virtual machine as a user-space process on the physical host. This provides an easy way to run multiple virtual machines on a single host.
Shared Kernel Virtualization Model
The Shared Kernel Virtualization Model is otherwise called System Level virtualization or OS Virtualization. It describes various implementations of running multiple, but logically distinct system environments on a single instance of an operating system kernel. That’s why it is called shared kernel virtualization model. It is also called shared kernel approach because all the virtual instances shared a common kernel of host operating system.
These are the various types of the virtualization techniques used at the moment.
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