The term “virtual” originates from the study of optics as it pertains to image reproduction. For instance, a mirror reproduces an image of an object, but because the image is not real and physical, it is deemed virtual. With this in mind, the concept of virtual machines (VMs) can be better understood. By applying virtualization software to a server, a separation between the server’s hardware and its operational ability can be achieved. In essence, the software creates a virtual “container” in which all the files of the server are duplicated and emulated. This software container or layer is called a hypervisor. With this in place, multiple virtual machines can utilize a physical server’s resources through the hypervisor even though each virtual machine may use a different operating system.
Traditionally, each physical server has its own IP address. A network accesses a server based on its IP configuration on the network. However, if that server becomes disabled, the network or portion of the network is inoperable until it can be repaired. In contrast, virtual machines have their own IP configurations, with each one having access to several physical servers that run the virtualization software. If one physical server becomes disabled, the virtual machines are thus still able to function normally by using the hardware and resources of other physical servers on the network. This high availability becomes an important issue in disaster-recovery situations.
The advantages of VMs clearly stem from the more efficient use of hardware resources, the elimination of underutilized redundancy in the IT system, and the ability to minimize downtime when servers malfunction. Larger organizations therefore enjoy greater advantages from such systems. As for disadvantages, indirect access of the physical server through the hypervisor is less efficient than direct access, and if multiple VMs are accessing a single physical server, variable performance may develop if workloads are high. While these issues may require specific attention, the advantages of virtual machines for large IT systems far outweigh the disadvantages.
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