Hardware Virtualization - Reasons For Virtualization

Reasons For Virtualization

• In the case of server consolidation, many small physical servers are replaced by one larger physical server to increase the utilization of costly hardware resources such as CPU. Although hardware is consolidated, typically OSes are not. Instead, each OS running on a physical server becomes converted to a distinct OS running inside a virtual machine. The large server can "host" many such "guest" virtual machines. This is known as Physical-to-Virtual (P2V) transformation.

• Consolidating servers can also have the added benefit of reducing energy consumption. A typical server runs at 425W and VMware estimates an average server consolidation ratio of 10:1.

• A virtual machine can be more easily controlled and inspected from outside than a physical one, and its configuration is more flexible. This is very useful in kernel development and for teaching operating system courses.

• A new virtual machine can be provisioned as needed without the need for an up-front hardware purchase.

• A virtual machine can easily be relocated from one physical machine to another as needed. For example, a salesperson going to a customer can copy a virtual machine with the demonstration software to his laptop, without the need to transport the physical computer. Likewise, an error inside a virtual machine does not harm the host system, so there is no risk of breaking down the OS on the laptop.

• Because of the easy relocation, virtual machines can be used in disaster recovery scenarios.

However, when multiple VMs are concurrently running on the same physical host, each VM may exhibit a varying and unstable performance, which highly depends on the workload imposed on the system by other VMs, unless proper techniques are used for temporal isolation among virtual machines.

There are several approaches to platform virtualization.

Examples of virtualization scenarios:

• Running one or more applications that are not supported by the host OS: A virtual machine running the required guest OS could allow the desired applications to be run, without altering the host OS.

• Evaluating an alternate operating system: The new OS could be run within a VM, without altering the host OS.

• Server virtualization: Multiple virtual servers could be run on a single physical server, in order to more fully utilize the hardware resources of the physical server.

• Duplicating specific environments: A virtual machine could, depending on the virtualization software used, be duplicated and installed on multiple hosts, or restored to a previously backed-up system state.

• Creating a protected environment: if a guest OS running on a VM becomes damaged in a way that is difficult to repair, such as may occur when studying malware or installing badly behaved software, the VM may simply be discarded without harm to the host system, and a clean copy used next time.