The pros and cons of a virtual desktop infrastructure

Desktops off the Rack


VDI, which appears to be unbeatably attractive at first glance, has one or two drawbacks upon closer inspection. These disadvantages include:

  • Costs: Reduced administration overhead saves money, and a thin client is significantly cheaper than a PC. However, you still need to do your sums, because new costs arise elsewhere. For example, additional costs for the VDI software with all the components for the required server hardware, plus storage and network costs, new devices, and the right application and operating system licenses (see the box "We Have Learned Much About Complexity") can easily eat up the savings.

We Have Learned Much about Complexity

Peter H. Ganten

Univention GmbH, offers one of the few open source desktop virtualization solutions. ADMIN magazine spoke to Peter H. Ganten, Univention's CEO and chairman of the Open Source Business Alliance (OSBA).

ADMIN: Desktop virtualization is a product that seems to be about to break year after year, but then does not really meet with wider acceptance. The advantages are obvious and impressive, but still only a small percentage of users rely on VDI. What reasons do you see for this?

Peter H. Ganten: Desktop virtualization is especially interesting in the Microsoft environment, but unfortunately, licensing Windows is anything but trivial. OEM or volume licenses cannot be used with it, and impractical restrictions apply to full versions. Customers must therefore purchase additional Microsoft Software Assurance and Virtual Desktop Access licenses. These are subscriptions that cause annually recurring costs. If you look at this over a five-year period, it is clear that this alone increases the cost of Windows by a few hundred euros per workplace.

In addition to this, mastering the topic often represents a significant challenge for IT departments, as concepts such as cloning images, copy-on-write, and the special requirements of software distribution must be understood and mastered to operate desktop virtualization successfully.

Finally, the Windows desktop today represents a bridging technology that is being replaced in particular by web-based applications. In many cases, organizations are better advised to invest in provisioning web-based software than in desktop virtualization.

ADMIN: Desktop virtualization competes with a number of other technologies that also rely on centralization and can use thin clients in part. They include [not only] the classic terminal server, but also streaming of the operating system or applications and managed or blade PCs. How would you classify desktop virtualization in this environment?

PHG: Yes, exactly. A large number of similar workplaces is often better served with traditional terminal server solutions; these solutions are easier to license, are less complex, and have lower hardware requirements.

Desktop virtualization is of interest where very individualized desktops need to be made available centrally. Blade PCs serve a similar purpose but are obviously much less flexible.

ADMIN: In traditional server-based computing you first think of jobs in administration, insurance companies, or banks. To what extent must a workplace be standardized to be suitable for desktop virtualization?

PHG: In our opinion, the most interesting market for desktop virtualization today is the education and training environment. Desktop virtualization offers the possibility to provision different desktops very fast depending on the teaching or training situation, or to save changing desktops for future learning sessions in order to provide other desktop environments in the meantime.

Limitations arise in particular with complex graphics applications as in games. To achieve good performance here, significant server resources and network performance are needed. Additionally, locally connected hardware can be a challenge in certain cases.

One alternative to server-side desktop virtualization is client-side desktop virtualization; virtual machines are executed directly on the client and only centrally managed. This eliminates the demands on the central server hardware, and graphics and hardware support are also usually better because the operations are handled locally and not over the network.

ADMIN: The VDI market is currently dominated by market leader VMware, with Citrix and Microsoft as runners up. Your company also offers a solution for desktop virtualization: Where do you see your niche market?

PHG: Two years ago, we released a desktop virtualization product with the aim to solve the many challenges associated with the topic in one fell swoop and, at the same time, learn as much as possible about the actual complexity of such solutions. This product was discontinued for the reasons mentioned. Instead of it, we are currently looking to provide a much leaner approach that gives administrators much more freedom.

This new approach can form the basis for integrating desktop virtualization with our solutions for schools and education authorities, as well as for project-specific implementations. In a later step we can also imagine providing virtualized desktops from the cloud for smaller organizations, where very low complexity and maximum flexibility are the requirements. We have not made any decisions on that.

  • Server dependence: The direct downside of centralization is server dependence. If the virtualization host fails, nothing works. Thus, you are forced not only to provide a powerful server but to make it highly available. The same applies to storage and the network  – they not only create costs, they add complexity.
  • Local hardware: If applications require locally available hardware, such as a USB document scanner or an external optical drive on the thin client, you need to research carefully whether you can loop this through the server, because it's not always possible.
  • Graphics and multimedia: Graphics-intensive applications, video, and audio are possible with thin clients, but you might need a special client that is more expensive, and you will certainly need much more network bandwidth. Additionally, state-of-the-art transmission protocols such as PCoIP (VMware) or HDX (Citrix), that handle such content more efficiently than the old ICAN (Citrix) and RDP (Microsoft) are the order of the day.
  • Morale: Many users feel downgraded if their fully equipped PC is replaced with a thin client that they cannot and are not allowed to manage. Psychological barriers should not be underestimated because, at worst, they lead to inner resignation and staff working to order.

A change from the traditional PC to the virtual PC must be planned carefully by the IT department because it has many consequences.

Side Effects

All resources previously distributed across the users' desks must be available centrally at the data center. This requirement does not simply mean a virtualization server with sufficient processing power – as a rule of thumb, you can expect a maximum of a dozen VMs per core if the workload is not very demanding. It applies in particular to storage for all the virtual disks in your virtual PCs.

Even if each virtual instance only uses 30 or 40GB, this setup quickly adds up to dozens of terabytes, and if you want to back up snapshots of the virtual instances, you need extra space. A SAN is useful, but not cheap. According to an analyst from Gartner, storage accounts for up to 60 percent of the VDI budget [5] – it's not only the capacity but also the performance that influences user acceptance.

The network should not use legacy 10Mb technology, which is often encountered in the form of small switches that are still running, even if everything else has been modernized. Each hardware bottleneck leads to poor performance and thus undermines the acceptance of the solution. Entirely new problems can arise if the desktops need to be delivered via WAN.

All components must also offer reserves and be scalable so that they can be adapted to meet future requirements, and 24/7 availability is a must-have. This requirement also applies to the network infrastructure, which must be redundant and carefully planned so that the failure of a single switch does not take down the whole environment. In some cases, you will even have to think about a geographically separate backup data center, or at least have a backup in another fire zone. At the end of the day, very high availability requirements are the price you pay for centralization.

Desktop virtualization does remove the need for the infamous admin sneakers. In this respect, however, work processes in IT also change. For administrators at the data center, demand increases as the IT environment becomes more complex. The cost of necessary skills training also counts toward the bottom line. In turn, you can possibly save money if you procure the work environment in the cloud as a desktop-as-a-service (DaaS).


Desktop virtualization unquestionably has the potential to contribute to a more efficient, more flexible, and greener IT (see the box "Biggest Advantage – Flexibility"). If the resources are correctly dimensioned, users also experience benefits at the workplace in terms of using a smaller, quieter, safer, less sensitive, and easily swappable device. To what extent all of these considerations make business sense is a completely different question. Whatever the answer, this brave new world does not come free of charge. Thus, you not only need to consider servers, storage, and networks, but also the increasing complexity and demands on the data center administration. Despite all your efforts, the equation might not balance out and return financial benefits. It is most likely to succeed in environments with highly standardized jobs and a manageable number of applications without extensive multimedia or graphics use. The expectation that VDI will blast all physical PCs into a black hole is deceptive.

Biggest Advantage – Flexibility

Christian Maurer

A well-known Citrix desktop virtualization customer is the Chamber of Commerce Würzburg-Schweinfurt, Germany. ADMIN magazine spoke to Christian Maurer, Head of IT Services.

ADMIN: Numerous benefits of desktop virtualization are obvious: Where do you achieve the biggest benefits and were your expectations met?

Christian Maurer: The biggest advantage that we see is flexibility. First, there are the increasing requirements for IT products from the departments. Today, we can customize solutions quickly and without great expense to match the respective environment. The second point is availability. Thanks to virtual desktops, each employee can be logged in to any device internally, and also externally by means of tokens, at any workplace.

ADMIN: What do you still have on your wish list? What future software development takes highest priority for you?

CM: We have a strong focus on application virtualization. I therefore hope for many new innovative developments in this technology. We also look forward to using the Xen client application, which has been on the agenda for years, to manage laptops more quickly and effectively in the future.

ADMIN: Was it difficult to convince your users to give up their own physical, full-fledged PCs? If there were reservations, how you were able to overcome them?

CM: The Chamber of Commerce Würzburg-Schweinfurt introduced a terminal server in the year 2000. In the course of this, the first thin clients were installed and older PCs converted to terminals. Over time, more PCs were replaced by thin clients. Since 2010, the Chamber of Commerce uses laptops only for employees with external contacts, we also have four fat clients for the two POS systems and the two switchboard workplaces. All other employees have thin clients. Since 2013, laptops have been replaced with iPads and thin clients. Because the thin client includes card reader and scanner functionality, there have been no reservations.

ADMIN: What changes has desktop virtualization meant to your IT organization?

CM: We can manage systems from anywhere in the world. The administrators have more time to focus on important tasks. Users also fully enjoy their new flexibility, so we have had to think about the availability of our IT systems outside normal working hours.

ADMIN: Different providers offer solutions for desktop virtualization. What made you decide to use a Citrix product?

CM: The crucial point was that Citrix has acquired a know-how advantage over the years. This is partly because of the very high transmission performance of content to the thin clients. This has been repeatedly confirmed by tests. Another advantage was the very attractive Citrix licensing policy, since we have used Citrix licenses for years.

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