How can organisations best approach desktop virtualisation? We already know about the benefits of virtualising server software, but the case for virtualising endpoint applications and operating systems can also be highly attractive. With malware reaching unprecedented levels, and with anti-virus software unable to catch all of it, the ability to refresh a desktop build easily from a remote helpdesk almost makes the case on its own. Then, there are other benefits, such as reduced hardware cost, and enhanced support capabilities for helpdesk staff.
That said, all desktop virtualisation is not the same. There are a variety of different models available to IT policy makers. Here are some of them:
Local operating system virtualisation
IT administrators can use a hypervisor, which is a small software 'shim' designed to provide an interface between multiple operating systems and the desktop or laptop computer's underlying silicon chip. This can be inserted into the computer's BIOS, and used to multiple operating systems on the desktop computer, or simply to easily maintain and reinstall standard operating system builds. It requires little or no extra server computing power, and desktops can operate without network connectivity.
Local application virtualisation
A single, non-virtualised operating system is maintained on the local machine, but each application runs atop a virtual layer, that presents a virtual set of resources, such as a virtual registry. This means that none of the applications alter the operating system's core resources, making it difficult, say, for a browser to infect the rest of the operating system if the user encounters a malicious web site. Although applications can be installed permanently on the local machine using this model, companies such as Microsoft are also offering products that stream applications to a local sandboxed environment, which can be instructed either to cache the application components, or to repeatedly retrieve them from the server when the user wants to run them.
Hosted virtual applications
A single instance of an application initially intended for single-person desktop use is hosted on a single operating system on a physical server, and made available to a group of people. This is the traditional model used throughout the nineties by Citrix.
Hosted shared virtual operating system
In this model, a single desktop operating system is hosted on a server, and accessed by a group of users. This model is typified by Microsoft's Terminal Services functionality in Windows Server.
Hosted dedicated virtual operating system
This is the model that most people think about when they talk about virtual desktop infrastructures. In this scenario, each user has access to a single virtual machine running on a server, that hosts a single operating system.
The benefit of the final scenario is that users can run applications that don't perform very well in shared mode, often making operations more reliable. There is a trade-off in terms of the hardware used, and enterprises adopting this model will generally find themselves using more powerful servers to achieve their goals.
Naturally, one of the biggest potential benefits for organisations adopting the hosted virtual desktop models is that they can reduce their hardware expenditure at the desk, minimising both the capital investment in powerful desktop hardware, while also reducing the costs involved with maintaining computers. However, there are downsides to this model. Gavriella Schuster, general manager of the Windows Product Management Group at Microsoft, warns that organisations must consider how much network connectivity they have when considering hosted models
. She also warns that additional storage and networking costs can more than offset hardware savings from virtual desktop infrastructure projects. She advises that VDI be restricted to specific use cases, such as shift-based task workers and contractors.
For companies considering virtual desktop integration, then, it is important to think about it as part of a wider approach to desktop virtualisation. Where you do wish to implement it, be sure to drive as much efficiency into back-end systems management as possible to reap the TCO benefits. Concentrating on automated princesses and highly virtualised servers will be an important part of any VDI plan.