Server virtualization is the most popular form of virtualization, and it is what most people think of when they hear the term. Server virtualization allows you to run one or more "virtual" servers on a single physical host system. As the power of hardware has increased in accordance with Moore's Law (which states that the number of transistors on a chip doubles every 24 months and, with it, computing power), businesses acquire ever-more powerful servers whether their applications require them or not. If our servers become much more powerful than the applications on them require (which most are) and our servers are not running anywhere near 100% capacity (most are running at 10% to 15%), then it makes sense to run multiple servers on a single machine.
Virtualization can be implemented in two different ways: software-based and hardware-based. Software-based virtualization is commonly implemented using either full virtualization or paravirtualization. In full virtualization, the hypervisor is independent of the operating system and sits between the operating system and the hardware. The hypervisor then acts as the gatekeeper between the multiple operating systems and the hardware to share system resources. In paravirtualization, the operating system is modified to be aware of the fact it is virtualized.
The advantage of using full virtualization is that any operating system can then be virtualized, while the advantage of using paravirtualization is that overall performance is better because the operating systems recognizes and cooperates with the hypervisor.
Hardware-based virtualization adds additional advantages, in that it makes the job of the hypervisor much easier if the hardware is designed with virtualization in mind. This allows for a much simpler, more efficient, and better performing overall virtualized system. Intel began offering its Virtualization Technology (VT) product in 2004, followed by AMD's Virtualization (AMD-V) product in 2006.
Server virtualization provides a host of benefits to both the IT department and to the users that they serve. These benefits include:
Improved investment utilization. Because many virtual servers can run on a single physical machine, you can greatly increase the utilization of your computer hardware investment, as well as reduce the number of physical servers required.
Decreased energy usage. Having fewer servers means less energy is needed to power and cool the servers.
More floor space. Reducing the number of servers can reduce the amount of space needed, or at least allow you to use the space more efficiently.
Decreased IT costs. Less physical equipment means fewer people are needed to keep it running. The cost of disposing of old equipment at end of life is also reduced.
Improved disaster recovery. By using virtual servers, you can create a "hot" standby image of the production machine that is much quicker to get up and running than is trying to restore backup tapes to a physical machine. The virtual standby image can sit idle on a
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