An insight into virtualization

In an ideal situation, a role/application would be installed on a Windows-based server (or any other OS platform), which may have been a blade or a rack server. As and when there was a further requirement, the number of physical servers increased, which also raised the requirement of real estate, maintenance, electricity, and data center cooling. However, the workloads were mostly underutilized, thereby causing a higher OPEX (short for Operational Expenditure).

Server virtualization software, better known as a Hypervisor, allows the abstraction of physical hardware on a server/computer and creates a pool of resources consisting of compute, storage, memory, and network. The same resources are offered to end consumers as consolidated virtual machines. A virtual machine is an emulation of a physical computer, and it runs as an isolated operating system container (partition), serving as a physical machine. At any point in time, there could be one or more than one virtual machine (VM or guest machine) running on a physical machine (host). Its resources are allocated among the VMs as per their specified hardware profile. The hardware profile of a VM is similar to real-life hardware specifications of a physical computer. All running VMs are isolated from each other and the host; however, they can be placed on the same or different network segments.

The equation for hosting the VMs is dealt with by the virtualization stack and the hypervisor. The hypervisor creates a platform on which VMs are created and hosted. The hypervisor ensures the capability of installing the same or different operating systems on the virtual machines, and sharing the resources that are deemed fit by hard profiles or dynamic scheduling. The hypervisor is classified into two types:

The following diagrams should illustrate these concepts better:

Figure 1-1: Differentiating the Type 1 and Type 2 Hypervisors

Storage virtualization allows abstraction of the underlying operations of storage resources and presents it transparently to consumer applications, computers, or network resources. It also simplifies the management of storage resources and enhances the abilities of low-level storage systems.

In other words, it introduces a flexible procedure, wherein storage from multiple sources can be used as a single repository and managed minus knowing the underlying complexity. The virtualization's implementation can take place at multiple layers of a SAN, which assists in delivering a highly available storage solution or presenting a high-performing storage on demand, with both instances being transparent to the end consumer. One closest example is offered with Windows Server 2012 and 2012 R2, called Storage Spaces. Storage Spaces enables you to abstract numerous physical disks into one logical pool.

Network virtualization is the youngest of the lot. Now, with network virtualization, it is possible to put all network services into the virtualization software layer. It introduced Software-defined networking (SDN), which uses virtual switches, logical routers, logical firewalls, and logical load balancers, and allows network provisioning without any disruption of the physical network while running traffic over it. So, it not only helps utilize the complete virtual network's feature set, from layer 2 to 7, but also provides isolation and multi-tenancy (yes, cloud!). This also allows VMs to retain their security properties when moved from one host server to another, which may be located on a different network. Network Virtualization using General Routing Encapsulation (NVGRE) is a network virtualization mechanism leveraged by Hyper-V Network Virtualization.

Desktop virtualization is a software technology that separates a desktop environment and any associated application programs from the physical client device that is used to access it. Each user retains their own instance of the desktop operating system and applications, but that stack runs in a virtual machine on a server that is accessed through a low-cost thin client. The fundamentals are similar to those of mainframes, which were later inherited by Remote Desktop Services (RDS; also known as Terminal Services) and finally evolved into true desktop virtualization, called Virtual Desktop Infrastructure (VDI). In principle, VDI is different from a remote desktop, and it is expensive. In VDI, users get their own small VMs from the desktop pool (Windows 7 or 8), whereas in the case of using a remote desktop, it's a shared environment with desktop experience of a Windows Server. In RDS, users can't customize their user experience as with virtual machines or real desktops.

Application virtualization allows applications to run seamlessly on unsupported platforms, or along with their own older or newer conflicting versions on the same device. There can be two variants for this, namely hosted or packaged: