VDI vs. terminal services: How to evaluate your use case before making a decision

Virtual desktop infrastructures have advantages, but there can also be unexpected costs and complexity. Colin Smith considers some of the questions you should answer before choosing VDI over terminal services or physical systems.

The last few years have seen a lot of hype around the virtual desktop infrastructure (VDI) space with some heavyweight players pushing their solutions. In reality, VDI is just a special case of remote desktop in which the user doesn't share a multi-user OS.  I've been a fan of remote desktops since I started working with WinFrame  over 15 years ago.  Since then, various flavours of terminal services have become a very mature, well understood solution.

With all of the momentum behind VDI deployments, organizations are beginning to realize that with the advantages come some unexpected costs and complexity.  One of the biggest challenges is managing VDI deployments. In theory they should be easier to manage than legacy physical desktops, but the management tools for physical desktops are very mature, well understood, and in many cases, already in place.

An unexpected side effect of this realization is that many organizations are re-evaluating whether Terminal Services (TS) might be a better fit for them than VDI.  As Brian Madden has said for years, it really comes down to understanding specific use cases.

Here are some questions to answer to help you understand your use cases and whether TS or VDI is an option over physical systems:


  1. What applications do your users need to run? This is the fundamental step in understanding your use cases. Without an understanding of what applications are in use and how important they are to your users, you can't make rational decisions about delivery models.
  2. Do they lend themselves to being run remotely in the datacenter? There are many reasons that applications may not be good candidates for remote execution. Consider applications like CAD/CAM or multi-media applications that are heavily resource intensive.
  3. Can the application run in a Terminal Server environment? Does the application require administrative rights to run? Does it require some special hardware like a dongle or USB key?  Does the user need to reboot the system or install drivers?

Application virtualization

Application virtualization like App-V and ThinApp can help overcome some of the application issues but they present challenges of their own:

  1. Is it even technically possible to virtualize / isolate / stream the app?
  2. Is application virtualization sufficient or does the virtual application need to be on a remote TS or VDI desktop?
  3. Do you need dynamic application installs?
  4. Do you have a stateless user environment or stateless desktop?
  5. Does everyone need the app, or just some users?
  6. How hard is the application to manage? Is it worth virtualizing?
  7. How many other apps will run locally in the context of this app?
  8. Do you need the raw application performance?

Other considerations

  1. Do users need to access the application from non-Windows clients?  What types of clients?
  2. Will the application ever need to be used from a client device with no network connection?
  3. Does the application need access to back-end data to be used? How much data?
  4. Do users need to start the application quickly from new devices?
  5. Does the application need to access data that's stored locally on the client device?
  6. Does the application need to integrate with other applications? Where are those other applications?
  7. Do you need to ensure that data stays off the client device?

Physical, TS or VDI?

Layering multiple virtualization techniques provides the possibility of eliminating many of the application compatibility issues that have been associated with terminal services in the past.

We often see multiple terminal servers running as VMS on a type 1 hypervisor and the applications running on the terminal server are virtualized using App-V or ThinApp.  If OS compatibility is an issue, Med-V can be used.

Physical devices are a good choice when you need raw performance or access to the physical hardware.  Until recently, If systems aren't always on the network TS and VDI were not options, but Citrix has recently started supporting offline VDI.

VDI is a good choice for environments where system state must be preserved, advance rights are required, or user isolation is an issue.

Most organizations will find that after analyzing and prioritizing physical and VDI use cases, the majority of use cases can probably be adequately serviced through TS.


Colin Smith is a Microsoft SCCM MVP who has been working with SMS since version 1.0. He has over 20 years of experience deploying Microsoft-based solutions for the private and public sector with a focus on desktop and data center management.


Colin makes some good points about the continued viability of Terminal Server. However, the bigger issue is that TS vs VDI does not have to be an either/or proposition. The fact is that Terminal Server has advantages over VDI, while VDI also has advantages over TS. That's why most organizations are best served by adopting a hybrid approach, with an optimal mix of TS (for task-oriented users), VDI (for power users), and Blade PCs (stock traders, graphic designers, etc.) which delivers the most benefit and platform flexibility to the organization. Ericom Software's PowerTerm WebConnect facilitates this hybrid approach by managing access to TS, VDI and Blade PCs, all with one management tool, one product. For more info on the hybrid approach visit: http://www.ericom.com/vdi_wts.asp?URL_ID=708 Adam

eli ben nun
eli ben nun

i think the right term here is ! Easier to make & Harder to break..


We have moved from desktops to LTSP Cluster. All our thin Clients are HP t5740 (WYSE is Shit) work perfectly. LTSP gives access to Linux (Ubuntu 10.4), Windows 2k3 Ent, Mac Xserve+aquaconnect for over 350 users. It is rock solid.


I've been looking at this very problem, though there are many good reasons to virtualise a desktop, for me it's more about reducing our 'foot print' through conserving power. However the new CPUs like the i3, i5 ,i7 and dual core atoms already go a long way to doing just that. So I am left with the simple question of does the up front costs justify rolling out a VDI to 350 machines? Suddenly it doesn't look as attractive. I'd like to point out that I am a strong advocate of server virtualisation............


You missed some critical decision points. - Where are your users in relationship to the VDI or TS servers? - What are your bandwidth constraints? - Does the user need off-line access? - Actual costs vs potential soft cost savings. Few of us get to claim soft cost savings in a cost study. The finance guys are all about actual costs. Physical, AppV, MedV, checked out VDI, VDI hosted on server and TS all have their strengths. Cost for infrastructure to support virtualization, the cost of a team to support virtualization, the cost of virtualization software, the licensing cost of the virtualized OS, the cost of patching tools, the cost of security tools, the cost of tools to manage the virtualization solution and the licensing of applications to run virtualized all add up. You most definitely need to do your homework and build a good business case for the various virtualization solutions. Those up front and continuing physical costs can be eye opening. Don't rely on virtualization to be the be all end all savior for your problems. All that said, there are areas where these virtual solutions are lifesavers.


I should mention that it is not uncommon for us to have 15+ concurrent users logged into a session. If I understand correctly, you are generally able to host more RDP sessions than VDI desktops on identical hardware.


We have 3 servers virtualized, 1 of which is a terminal server (RDS as of W2k8) with all the mission-critical apps installed. If I ever have problems with the TS, I just roll back to a previous snapshot. Works great. All thin clients are Wyse V10L's...with the newest Wyse firmware there are not nearly as many issues with Flash and other multimedia performance. Bottom line: TS is serving us well and gives us very little grief. It is unlikely we'll move to VDI in the near future.

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