Virtualization

Virtualization allows multiple operating system instances to run concurrently on a single computer, it is a means of separating hardware from single operating systems. Virtualization uses specialized software designed to allow multiple operating systems to run concurrently. Each Virtual Server act like a unique physical device, capable of running its own operating system. In simple terms, virtualization (or virtualisation) is the creation of a virtual (rather than actual) version of something, such as a hardware platform, operating system, storage device, or network resources. Virtualization lets a single physical resource (such as a server, an operating system, an application, or storage device) appear as multiple logical resources; or making multiple physical resources (such as storage devices or servers) appear as a single logical resource.

Virtualization can be viewed as part of an overall trend in enterprise IT that includes autonomic computing, a scenario in which the IT environment will be able to manage itself based on perceived activity, and utility computing, in which computer processing power is seen as a utility that clients can pay for only as needed. The usual goal of virtualization is to centralize administrative tasks while improving scalability and work load.

For example, a Windows computer with VMware Workstation or Hyper-V installed can run Linux within the Windows interface. Similarly, a Macintosh computer can use Parallels Desktop to run Windows within the Mac OS X interface. When another operating system (OS) is running on top of the main system, it is called a "Virtual Machine (VM)." This is because it acts like a typical computer but is actually running on top of another operating system.

Virtualization software acts as a layer between a computer's primary OS and the virtual OS. It allows the virtual system to access the computer's hardware, such as the RAM, CPU, and video card, just like the primary OS. This is different than emulation, which actually translates each command into a form that the system's processor can understand. Since Macintosh and Windows computers now both use the "x86" processor architecture, it is possible to run both OSes on the same machine via virtualization, rather than emulation.

Why use Virtualization ?

Consolidation :

It is a common practice to dedicate each server to a single application. If several applications only use a small amount of processing power, the network administrator can combine several machines into one server running multiple virtual environments. For companies that have hundreds or thousands of servers, the need for physical space can decrease significantly.

This saves on:

·         Cost : 10000$ per maintenance cost per machine

·         Space: Less servers, less space needed

·         Energy: Savings by upto 80%

·         Environment: Reduced CO2 emissions due to decrease in number of servers

Redundancy

Server virtualization provides a way for companies to practice redundancy without purchasing additional hardware. Redundancy refers to running the same application on multiple servers. It's a safety measure -- if a server fails for any reason, another server running the same application can take its place.

This minimizes any interruption in service. It wouldn't make sense to build two virtual servers performing the same application on the same physical server. If the physical server were to crash, both virtual servers would also fail. In most cases, network administrators will create redundant virtual servers on different physical machines.

Legacy Hardware

Server hardware will eventually become obsolete, and switching from one system to another can be difficult. In order to continue offering the services provided by these outdated systems – some times called legacy systems -- a network administrator could create a virtual version of the hardware on modern servers. From an application perspective, nothing has changed. The programs perform as if they were still running on the old hardware. This can give the company time to transition to new processes without worrying about hardware failures, particularly if the company that produced the legacy hardware no longer exists and can't fix broken equipment.

Migration

An emerging trend in server virtualization is called migration. Migration refers to moving a server environment from one place to another. With the right hardware and software, it's possible to move a virtual server from one physical machine in a network to another. Originally, this was possible only if both physical machines ran on the same hardware, operating system and processor. It's possible now to migrate virtual servers from one physical machine to another even if both machines have different processors, but only if the processors come from the same manufacturer

Segregation

Virtual servers offer programmers isolated, independent systems in which they can test new applications or operating systems. Rather than buying a dedicated physical machine, the network administrator can create a virtual server on an existing machine. Because each virtual server is independent in relation to all the other servers, programmers can run software without worrying about affecting other applications .

In the traditional concept we require a dedicated single physical server for each Operating systems. These operating system store the required application like Email server, Web Server, database server, etc. So if we requires to run 20 application and 20 operating system, then we have to installed 20 physical server with 20 operating systems. This scenario required huge hardware cost and space cost.

 

Now we can run multiple operating systems and application on a single physical machine with the helps of virtual machine. We can create multiple virtual machine as per requirement and hardware support.

Terms

Host OS/Machine : It is the actual machine or OS on which Virtualization takes place.

Guest OS/Machine : It is the actual Virtual machine or OS.

Hypervisor : he software or firmware that creates a virtual machine on the host hardware.

Types of Virtualization

·         Full Virtualization 

·         Para Virtualization

·         OS Virtualization

Full Virtualization

Full virtualization uses a special kind of software called a hypervisor. The hypervisor interacts directly with the physical server's CPU and disk space. It serves as a platform for the virtual servers‘ operating systems. The hypervisor keeps each virtual server completely independent and unaware of the other virtual servers running on the physical machine. Each guest server runs on its own OS -- you can even have one guest running on Linux and another on Windows.

 

Para-virtualization

The para-virtualization approach is a little different than the full virtualization technique, the guest servers in a para-virtualization system are aware of one another. A para-virtualization hypervisor doesn't need as much processing power to manage the guest operating systems, because each OS is already aware of the demands the other operating systems are placing on the physical server. The entire system works together as a cohesive unit.