Virtualization consists in inserting an abstract layer between the client and a provider. In the world of Information Systems, it uses the technical resources (hardware/software) to operate separately and on one physical machine, multiple operating systems and applications, as though they are running on one different physical machine.
1- Pros of virtualization:
Today, the applications that we use demand a huge amount of resources but paradoxically take only a fraction of the potential of some servers.
According to Microsoft, it is very often possible to combine more than five servers on one machine without there being any performance anxiety.
Thus, we deduct that virtualization has various advantages :
- It reduces the number of physical machines, which results in a return on investment.
- Regarding the required space, a server is capable of running different operating systems on one machine, it reduces up to half of the space dedicated to an enterprise’s servers.
- In addition of this increased space, less physical machines means a reduced electricity consumption.
- It allows a fast and simple server administration.
- Before, applications were tightly linked to the servers on which they are running. Virtualization creates an abstract layer between the physical hardware and the software, it allows the execution and the co-existence of different servers on one physical machine. Thus, the applications running on an older operating system (for instance, NT4), can be stored without maintaining the constraints of the previous physical server.
- Virtualization reduce the charge on the administrators as well as the time and costs spent on the server administration.
- It simplifies the implementation, the testing, and production of platforms.
- And to finish, it increases high availability of the servers.
We can add these functions to a more secure network. The machine that hosts the virtual systems is not visible to hackers.
2- Cons of virtualization:
In spite of all these advantages, embarking towards virtualization without fully thinking and studying, and most importantly without making a recovery plan in case of a disaster ( Disaster Recovery Plan), can be fatal to your Information System.
- Virtualization implementation induce a certain complexity of administration, and brings more risks that can be found in any virtual environment. This is another way to organize one’s machines, which can demand a certain amount of time for adjustment.
- Another problem: data administration. How to find one’s data when they are shared throughout many physical disks, but stored on logical volumes? It is imperative to make a detailed map of one’s data in a time T. The LUNs (logical Unit Number) has to be normalized, a name and number.
- Finally, if the machine that hosts all the operating systems stops, the situation can quickly become a nightmare. Especially that virtualization often disguise the origin of the failures, including functionalities as automatic load balancing, which makes these failures virtually invisible, and despite all of this, the system will carry on functioning. But if a bigger error occurs, it becomes almost impossible for the administrator to localize it.
For a redundant virtualization, it is essential to duplicate the virtual machines. In every case the virtualization should not be taken lightly and has to be considered with neat attention and vigilance.