Virtualization Explained

By Sanjay Srivastava
Updated: July 09, 2013

Virtualization Explained

A hybrid virtual desktop infrastructure (VDI) model improves upon the limitations of distributed client computing. But is VDI still viable with public cloud computing taking off?

Virtualization helps in autonomic (self-managing) computing by creating a virtual version of a storage device, hardware platform, operating system (OS), or network resources. It also centralizes administrative tasks allowing several operating systems running simultaneously on a single CPU. Unlike multitasking, where several programs run on the same OS, this parallelism offers several benefits. It is economical, improves scalability and hardware-resource utilization, offering a faster provision of mission-critical applications.

In hardware virtualization - also called platform virtualization - software can be run on virtual machines (also called guest machines) separate from the underlying hardware resources. The virtual machine looks and acts like a computer with an operating system. While the virtualization takes place on the host machine, the software that creates a virtual machine on the host hardware is a virtual machine monitor or hypervisor. In full virtualization, the actual hardware is completely simulated allowing the guest operating system to run unmodified. However, in partial virtualization, part of the target environment is simulated with some guest programs running in this virtual environment. In paravirtualization, guest programs are specifically modified to run in their own isolated domains without simulating the hardware environment.

Specially designed hardware components may also be used to boost the efficiency of hardware virtualization. Hardware-assisted virtualization employs a piece of software called a hypervisor that either copies the behavior of a piece of hardware or the entire computer. This is what sets it apart from hardware emulation, where a piece of hardware emulates another part of the computer's hardware. The domain of use of a hypervisor is different from an emulator.

Desktop virtualization allows the user to interact with the host computer via internet or a local area network. This gives way to the added advantage of multiple clients simultaneously hosting virtual machines with the host acting as the server. With storage secure in the data center, the VDI model allows applications to be hosted on servers for virtual clients. Thus, the clients have the flexibility to access their desktop from any location and get remote desktop services (RDS). This converged infrastructure centralizes resources helping in easier management for administrators. It provides scalability, flexibility and changes can be quickly implemented. Multiple users can simultaneously log into a single computer via internet through session virtualization. In generic VDI the desktop operating system can be contained within a virtual machine that runs on a centralized server hypervisor in the data center. Leaders in VDI like Citrix offer both aforementioned techonologies to users.

Besides hardware virtualization, software virtualization also offers several choices. Multiple virtualized environments can be hosted in a single operating system. Individual applications can also be hosted separately from the underlying operating system. Specific components, especially those that may be under review for development purposes, can be virtualized by Service Virtualization. A memory pool is created using Memory Virtualization which centralizes all the RAM resources over a network with virtual memory serving adjoining working memory and separating it from the underlying physical memory.

Storage virtualization concepts enhance functionality and enable more advanced features by providing a simple interface. They add a new layer of hardware and/or software between servers and storage systems, enabling easier management of storage devices. Different levels of SAN can employ this technology with software applications or by using hardware and software hybrid appliances. Files from different hosts can be accessed online through the distributed file system. This system also ensures data privacy as clients do not have access to underlying data storage. This kind of system offers options of transparent replication, and in case a few nodes do go offline, the system continues to work without any data loss. Among storage virtualization software, a storage hypervisor virtualizes storage resources and manages them, thus catering to the needs of each individual environment.

After virtualizing servers, now data centers and even networks are catching up. Similarly, data, databases, applications and data services vendors can also be abstracted through a single data access layer. Hardware resources can be shared more efficiently between applications and clients using database virtualization. Networks can be combined into a virtual unit externally or internally by providing functionality akin to a network to the software in a system.

However, to make the transition to virtualization a smooth ride and avoid cloud stall, gaining a tangible perspective and proper planning is imperative. The actual cost of virtualization should be planned beforehand, keeping in mind ROI analysis and depreciation value of hardware before switching to cloud services. Virtualization does not lead to a decrease in or complete loss of IT functionality, and secure networks are still needed and integrated with the new cloud services.

Viewing the flip side of the coin, VDI poses some challenges. VDI brings along the hidden costs of virtualization: software licensing, cost outlay for server hardware, VPN appliances, management software and storage requirements. It also demands network upgrading and a possible problem of VM sprawl. Many VDI projects are thwarted at the pilot stage due to high costs. Though it is not possible to exactly quantify the hidden costs associated with VDI implementation, it may yet be worth it for a business if it gets increased productivity from its users and more ROI. It makes sense to review and realign company policies for the new virtual environment.

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