Introduction
At its core, there are two major types of virtualisation: Type 1 and Type 2. There are complaints attached to these labels, and there are hybrids that defy them, but by and large they serve their purpose in helping us to categorise virtualisation.
Type 1 is known as a native, or 'bare metal' hypervisor. It requires no operating system to be preinstalled — it is one, just in a very stripped-down form. If your intent is virtualisation alone, this is the most efficient type, allowing access to the hardware through the hypervisor.
Type 2 on the other hand, is run on a preinstalled operating system. It's also known as hosted virtualisation or a virtual machine monitor (VMM). You'd likely run this when you need the host OS's features to have access to your hardware. For example, you may want to run on Solaris to give direct access to creating a RAID-Z array. Or perhaps you need to run on Windows, to give a virtualised operating system access to a hardware device that usually only Windows can see. Or maybe you just want to test out a new OS before doing a roll-out — either way, different virtualisation suits different needs.
In this round-up we'll be looking at Type 1 virtualisation solutions from the market leaders: Microsoft, Citrix and VMware. In the coming weeks we'll look into Type 2 competitors Parallels, VirtualBox, VMware Workstation and a few odd tools that aren't quite virtualisation, but do get binaries running across different OSs.
Bare metal hypervisors
In today's market, VMware still retains dominant share, but others are starting to move in on its lead, including XenServer from Citrix and Hyper-V from Microsoft. Both have received a large amount of press and also support from the industry. Of course, there are other Xen-based solutions such as xVM Server from Sun and Red Hat Linux Enterprise (RHEL) Server, which currently include virtualisation (although RHEL will be moving to KVM later in the year, as Ubuntu did last year). For this review, our focus was primarily on VMware ESXi 3.5, XenServer 5 and Hyper-V R2 beta (more on why later).
