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Understanding Microsoft Virtualization Solutions, From the Desktop to the Data Center, 2nd Edition
own virtual machine and is allocated logical instances of the computer’s processors, hard disks, network cards, and other hardware resources. An operating system that is running in a virtual machine is unaware that it is executing in a virtual environment and behaves as if it exclusively controls the underlying physical computer’s hardware. Realizing virtual machines as described in the preceding paragraph means that server virtualization must be implemented in a way that meets the following requirements: n
Management interfaces Server virtualization requires management interfaces so that administrators can create, configure, and monitor virtual machines running on the computer. These interfaces should also support programmatic administration, and they must be able to work over the network so that virtual machines can be managed remotely.
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Memory management Server virtualization requires a memory manager, which ensures that each virtual machine receives its allocation of memory resources and that those memory resources are isolated between each virtual machine.
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Scheduler Server virtualization requires a scheduler to manage access to physical resources by different virtual machines. The scheduler must be configurable by the administrator so that different virtual machines can be given different priority to hardware as might be needed.
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State machine Server virtualization requires a state machine that can track information concerning the current state of all virtual machines on the computer. State information for a virtual machine includes its CPU, memory, devices, and whether the virtual machine is running or stopped. The state machine must also be designed to manage transitions between different states.
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Storage and networking Server virtualization requires functionality that can abstract storage and networking resources on the computer so that each virtual machine is presented with the view that it owns its own exclusive hard disks and network interfaces. In addition, machine virtualization must be able to multiplex access to physical devices in a way that is consistent, isolated, and secure.
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Virtualized devices Server virtualization requires virtualized devices that can provide operating systems running in virtual machines with logical representations of devices that behave in a similar manner as their physical counterparts. In other words, when an operating system running in a virtual machine needs to access a physical device on the computer, it does so by accessing a corresponding virtualized device, and this virtualized device is accessed in the same manner as a physical device would be accessed.
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Virtual device drivers Server virtualization requires that virtual device drivers be installed on operating systems running in virtual machines. These virtual device drivers enable applications to access the virtual representations of hardware and I/O connections in the same manner that they would access hardware and I/O connections on the underlying physical hardware.