What is virtualisation?

Bryan O'Connor explains what a virtual machine is and what the benefits of virtualisation are for any organisation.

Many times I’m asked, “So, what do you do for a living?” and I reply, “I’m a virtualisation and cloud trainer.” This is then met by blank looks, and that’s fine.

I started working with VMware in 1999, one year after they became a company, and I’ve worked with them ever since – in fact, I’m a member of their Customer Technical Advisory Board for Cloud and Infrastructure. VMware is the leading on-premises virtualisation hypervisor.

So let’s start with what virtualisation (more commonly spelt virtualization) is and what a hypervisor is, and then I'll explain why we use it in IT.

What is virtualisation? And what is a virtual machine?

Virtualisation is the concept of recreating a computer in software. We then run that virtual machine (VM) on a server that is running a hypervisor, which is software that allows lots of virtual machines to run side by side on the same physical server.

A virtual machine can be considered to be a software representation of a physical machine and its hardware components – it will have virtual processors, virtual memory, virtual storage and virtual network adapters. Every VM has virtual devices that provide the same functionality as physical hardware but are more portable, more secure, and easier to manage.

As the virtual machine is software, this means that all of those components are literally a collection of files working together to perform the functions of the virtual machine.

A VM includes a set of specification and configuration files and is supported by the physical resources of a host. 

Virtual machine components

The benefits of virtualisation

Virtual machines are:

  • Easy to move or copy as they are just files.
  • Independent of physical hardware because VMs are encapsulated into files isolated from other VMs running on the same physical hardware.
  • Insulated from physical hardware changes, so a change to the hypervisor hardware does not automatically change the virtual hardware.

In a physical machine, the operating system is installed directly on the physical hardware. The operating system requires specific device drivers to support specific hardware. If the computer is upgraded with new hardware, new device drivers are required and this could cause the operating system to not load, or become unreliable.

If applications interface directly with hardware drivers, an upgrade to the hardware, drivers, or both can have significant repercussions if there are incompatibilities. Because of these potential issues, the IT department must test hardware upgrades against all software.

Virtualising these systems saves on such costs because VMs are 100% software.

Multiple VMs are isolated from one another. You can have a database server and an email server running on the same physical computer. The isolation between the VMs means that software-dependency conflicts are not a problem. Even users with system administrator privileges on a VM’s guest operating system cannot breach this layer of isolation to access another VM.

As a result of VM isolation, if a guest operating system running in a VM fails, other VMs on the same hypervisor host are unaffected and continue to run. A guest operating system failure in one virtual machine does not affect access and performance:

  • Users can still access the other VMs.
  • The operational VMs can access the resources that they need.
  • The other VMs can still perform.

With VMs, you can consolidate your physical servers and make more efficient use of your hardware.

  • You can rapidly and consistently provision VMs.
  • With VMs, you can use live migration, fault tolerance, high availability, and disaster recovery scenarios to increase uptime and reduce recovery time from failures.
  • You can use multitenancy to mix VMs into specialised configurations, such as a DMZ.
  • With VMs, you can support legacy applications and operating systems on newer hardware when maintenance contracts on the existing hardware expire.

Image: Physical server and virtualisation system

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