Definition of Virtual Machine
A conventional computer has a single OS image. This offers a rigid architecture that tightly couples application software to a specific hardware platform. Some software running well on one machine may not be executable on another platform with a different instruction set under a fixed OS. A Virtual machine (VM) offer novel solutions to underutilized resources, application inflexibility, software manageability, and security concerns in existing physical machines.
Today, to build large clusters, grids, and clouds, we need to access large amounts of computing, storage, and networking resources in a virtualized manner. We need to aggregate those resources, and hopefully, offer a single system image. In particular, a cloud of provisioned resources must rely on virtualization of processors, memory, and I/O facilities dynamically.
However, the basic concepts of virtualized resources, such as VMs, virtual storage, and virtual networking and their virtualization software or middleware, need to be introduced first. Please read the architectures of three VM configurations.
Building Virtual Machine Images
Building virtual machine images is a straightforward task, but we must be careful to analyze application dependencies to ensure all necessary supporting software is in place. Also, different configurations of an application may require different versions of supporting libraries, so we may need to support several versions of similar images. Applications may have different configurations depending on how the application is used, and this could also warrant having multiple versions. For example, a Java application server may be configured differently if we expect heavy, moderate, or light use. Rather than expect
Storage Virtualization for VM
Storage virtualization, like server virtualization, abstracts the services provided by hardware. Consumers of these services can allocate resources without concern for implementation details. For example, details like the logical unit number (LUN) mappings to storage volumes and storage devices are managed by storage virtualization software. When persistent storage is needed, the cloud services consumer simply makes a call to a programming interface specifying the amount of storage required.
Local vs. Cloud Storage
Virtual machine instances can provide local storage for temporary storage during the life of the virtual machine instance. The data in this storage is lost when the virtual machine is shut down. The persistent cloud storage described here is provided by devices that are independent of virtual machines. Multiple virtual machines can access the same storage blocks and the data continues to exist regardless of how virtual machines are started and stopped.
