What you need to know about Server Virtualization?
Server virtualization is not a new technique. For decades now server virtualization existed but it is only in the recent year’s server Virtualization has entered the world of Information Technology (IT). It is a still a new technology and several companies out in the market offer different approaches. Server virtualization is a hot topic in the IT world and it is expected to take the market by storm in the coming years.
Server virtualization is the process of masking of resources of the servers including processors, operating systems and number and identities of individual physical servers. The process takes place through a software application where the server administrator divides one physical server into multiple isolated virtual environments. These isolated virtual environments are called virtual servers and at times they are also known as guests, emulations, instances or cis.
There exists mainly three different ways of approach to server virtualization and they are “Virtual Machine Models”, “Virtualization at the operating system level” and “Paravirtual Machine Model”. In this article, we will read about these three approaches a little more deeply for everyone’s better understanding of the Server Virtualizationhnique.
- Virtual Machine Model– Virtual machines are mainly based on the guest paradigm where each guest runs on an imitation (virtual) of the hardware layer allowing the guest operating system to run without any modifications. The guest does not know about the operating system of the host as it is unaware of the fact that it is running on an imitation of the real hardware.
A hypervisor is used to coordinate instructions to the CPU as it requires real computing resources from the host. This hypervisor is called the Virtual Machine Monitor (VMM) and the model is based on this machine. The VMM manages all the executed codes that require extra privileges and also validates all the guest-issued CPU instructions. Microsoft Virtual Server and VMware both use the virtual machine model approach.
- Virtualization at OS level– This approach is a bit different and is not based on host/guest paradigm. In this model, a single OS kernel is run by the host at its core and the operating system functionality is exported to each of the guests.
It is important that the guest and the host use the same operating system but different distributions of the same system are allowed. This distribution architecture reduces CPU usage overhead by eliminating system calls between different layers. Virtualization at the OS-level has the ability to host thousands simultaneously. Solaris Zones and Virtuozzo uses OS-level virtualization.
- Para-Virtual Machine Model– The Para Virtual Machine Model or the PVM model is also based on host/guest paradigm using virtual machine monitor as well. In this type of model, the VMM actually modifies the codes of the guest operating system. This process is called “Porting”.
Porting utilizes privilege system calls sparingly by supporting the VMM. Likewise Virtual Machines, Para-Virtual Machines are also capable of running multiple operating systems. Para Virtual Machine model is used by a number of organizations. XEN and UML both uses PVM model.