Mini-Guide to virtualisation

Pre-virtualisation - The way it used to be done

To understand the benefits of virtualisation you need to appreciate the difference between a physical server and the roles that server fulfils.

Traditionally a physical server, I.e. the box itself, ran one server operating system (O/S). Be it server 2000, 2003 or Small Business Server the physical machine could only ever run one O/S at any one time but that operating system could have one or more distinct roles.

Roles include running as a file server, e-mail server, domain controller etc and the more roles you put on a server the more work it has to do simultaneously - sharing CPU time and memory space between each role. This causes problems when two or more roles vie for resources. To complicate matters, certain roles can not be installed on the same O/S due to conflicts or security issues.

This is why even mid-sized businesses may have several servers. Each server responsible for a specific role.

The virtualisation age

A virtual machine is basically a software implementation of a physical computer. This software computer can be used like a real computer in every way, it can have an O/S installed on it and it can run one or more roles just like a real computer.

Virtual machines run on a server configured for this purpose - called a hypervisor. The real benefit from virtualisation is that one physical box configured in this way can run any number of virtual machines without those virtual machines conflicting. This means that one box can support multiple computers running roles that previously needed to be run on separate hardware.

By using virtual machines it's possible to run an entire network on a single physical machine with no conflicts between roles and far greater utilisation of resources.