Server consolidation – virtualization

Server Consolidation
Even though Server Consolidation has it’s own meaning for the objective of the exam has a completely different point of view. Don’t believe that server consolidation is the same as server consolidation but have to recognise that both share the same goals.

In old days when you work on a server consolidation project the main idea was to take some servers that run similar services and consolidate them on fewer. The idea of server consolidation was to reduce space, energy consumption and operative costs.

By reducing the amount of servers in the data center there were less energy consumption, less heat so less energy required to refrigerate the environment. Also as fewer servers were in place less people were required to manage those. But, and always there is a but, it didn’t have the advantages of server virtualization.

Server virtualization
With almost 15 years of experience in different IT fields as technical support, windows administrator, Microsoft consultant and vmware consultant among others I can say that since vmware appeared the day to day work changed drastically.

Why? because the benefits that server virtualization introduced simplified the way we design, operate and manage IT.

In essence the idea behind server virtualization is the same of server consolidation but with some differences. Basically server virtualization let’s you run several virtual servers (virtual machines) inside one big physical server but keeping independence of the operative systems that run inside the virtual machines.

For example with server consolidation if we had eight file servers we would consolidate those servers on four. But, those four servers would be running the same operative system because on a server consolidation project you always tried to standardise the operative system.

Instead, on server virtualization you keep the original operative system inside the virtual machine and, if you want, you could make a virtual copy of the original physical servers on the vm using a process called Physicall to Virtual or P2V.


server virtualization


Depending of the type of server virtualization that you chose there are independency between the virtual machines that run on the physical server. With that if the operative system that runs on one virtual machines crashes the others remain working properly without being affected.

In order to add some vocabulary that is important server virtualization here is a list of common terms that you need to know:

Hypervisor: Is the “engine” (software) that allows the virtual machines. Depending on the type of virtualization that you are using the hypervisor can run on top of an existing operative (Windows or Linux for x86 systems) system or directly on top of the hardware. Running a hypervisor on top of an operative system is no longer in use on new deployments.
Host: is the physical server where the hypervisor is installed.
Guest: is the operative system that runs inside the virtual machine. 

Of course that there are some cons on server virtualization but those will be addressed on another post.

Types of server virtualization

A few different types of server virtualization exists today, each and everyone has it’s advantages and disadvantages. It would depend on your needs which one is the best for your environment.

The most common types of server virtualization are:

  • Full virtualization
  • Hardware-assisted virtualization
  • Paravirtualization

Full virtualization
In full virtualization the guest operative system runs unmodified on the virtual machine and every virtual machines is isolated from each other. An example of Full virtualization is vmware server.   

Hardware-assisted virtualization
This technology first appeared on 2006 with the introduction of Intel Virtualization Technology (VT-x) and AMD-v from AMD that allowed the controller of virtual machines to run below ring 0. these technologies allowed applications to trap sensitive and privileged  calls directly to the hypervisor removing the need of using binary translation (Full virtualization) and Para virtualization.  An exaplme of Hardware-assited virtualization is vmware ESXi.

OS-assisted or Paravirtualization

On Paravirtualization the guest operative systems needs to me modified in order to replace non-virtualizable instructions with hypercalls that communicate directly to the virtualizaton layer.

Paravirtualization is different from full virtualization, where the unmodified OS does not know it is virtualized and sensitive OS calls are trapped using binary translation. The value proposition of paravirtualization is in lower virtualization overhead, but the performance advantage of paravirtualization over full
virtualization can vary greatly depending on the workload.

For more information about the different types of virtualization please check Understanding Full Virtualization, Paravirtualization, andHardwareAssist  

Server consolidation – virtualization belongs to Explain the purpose and application of virtualization technology  domain of Comptia Green IT Certification.