In many a desktop virtualization project, there will be a 
discussion around the type of desktop virtualisation to use. Before you even get to the entertaining “Citrix vs VMware vs Other” quasi-religious debate, there will be a VDI vs RDSH altercation. It can altercate for days. Ultimately, no business question gets asked, nor decision made, as technical stags lock antlers. It is not unusual for this debacle to be silenced by someone simply getting tired of the PoC posturing and rolling out pallet loads of new PCs.
If any year is to be the year of virtual desktops, then it is not just simply a question of having nifty appliances, but also of having a better understanding of desktop virtualization solutions. A recent article from the BBC website on common language gave the ultimate benefit of a common understanding as “world peace”. If a better understanding between people can bring the laudable hope of goodwill unto man, then surely an easier corporate upgrade and better application access will be a mere bagatelle?
The options for purchase for VDI or RDSH, VDI or Terminal Services, for hosted desktops or session desktops are all the same conversation. RDSH is indeed on the back foot through regular re-marketing of terms. Presentation Virtualization Terminal Services and RDSH are the same thing: a multi-user server OS capable of hosting applications and desktops to remote users.
Increasingly, desktop virtualization vendors are ensuring they sit between both VDI and RDSH camps. Citrix obviously – XenApp and XenDesktop. In our Presentation Virtualization whitepaper, every RDSH vendor has a VDI option. But also, “traditional” VDI vendors are being more savvy. Desktone offers a RDSH option. Teradici has delivered on their promise and recently announced Teradici Arch, a software solution for RDSH.
What are the similarities and differences between VDI and RDSH? What can calm everything down and make the combatants think about what it is that they have done?
What is VDI?
VDI is a Virtual Desktop Infrastructure. VDI is:
- A Remoted Desktop OS that runs on virtualized servers.
Desktop operating systems and applications run inside virtual machines that reside on servers in a data center.- Desktop instances are virtualized using products such as Citrix XenServer, Microsoft Hyper-V, and VMware vSphere.
- Compute, memory, and storage resources are consolidated and presented to a variety of endpoints with a range of license options.
- Users interact remotely with the desktops using hardware or software clients with a remote display protocol over standard IP network connections.
- Typically VMware View or Citrix XenDesktop – although you’ve the likes of Desktone, Dell/Quest vWorkspace, Ericom, Verde, 2X, and indeed Microsoft’s Remote Desktop Services (RDS) (hosted desktops or a naked virtual desktops, i.e. a virtual desktop without third-party features)
What are the advantages of this technology? To call out some of the main ones – when configuring the virutalised environment, simple things like desktop engineers and applications users see a desktop OS they understand. Importantly, users can be given greater control of the VM environment. That instance can be dedicated to them, they could be the administrator of that environment—different VMs can have different specifications.
Disadvantages? A desktop OS is historically not designed to run on a multi-user platform: hardware sizing can be tricky (and a reason for the rise in interest in appliance vendors). Microsoft licensing for the VM instances is focused on ensuring the impact on OEM device suppliers is minimised. Properly licensing VDI for Microsoft desktop OSes can be expensive if the end points are not assigned an Microsoft enterprise desktop license. Printing, network bandwidth for delivery of services, and access to data.
Like a ride in a taxi, the environment is dedicated to you; you can decide to change the journey specification. An environment where there is diversity of user environments favors VDI.
What is RDSH?
Microsoft Remote Desktop Sessions Host (RDSH). You could have asked what is Presentation Virtualization, what is Terminal Services. Still, what is that? 
- A multi-user server operating system such as Windows 2008 R2.
- Able to host complete desktop sessions.
- RDSH is a Windows Server role service.
- Each RDSH server runs a single instance of the OS.
- The server OS is Multi-session, but there each server has a single stack of application software that the users share.
- RDSH servers can run without server virtualisation, although they are increasingly being virtualized.
- RDSH services can also publish applications (e.g. Microsoft RemoteApps, Citrix Published Applications) as well as publish desktops. What this means is that the application is hosted on the server in the datacentre, but the user is presented not with a desktop running the application, but a remoted view of the application. To the user, it appears as if the application is running in their own desktop environment.
What are the advantages as of this technology? When configuring the environment, the complexity is reduced. 50 users can share 1 instance of Microsoft Office on one OS.If you’ve a mobile laptop (non-Microsoft), its simply delivery schedule with the onus on the business unit/user to clarify those instances.
Disadvantages? Admins and application vendors can baulk at a running applications designed for Windows desktops on a server operating system. Given the multi-user environment – one change impacts many. While this can be a benefit (in terms of fast delivery) – users should be restricted from making changes to the application set, users can personalize – environments can’t be customized for individuals.
Like a ride in a bus, it is very efficient for servicing lots of users. You don’t all have to make exactly the same journey, but everyone needs to be going in the same direction. Uniformity of user activity favors RDSH. You can learn more about RDSH in our Presentation Virtualization Solutions whitepaper
Winning Hearts and Minds
Both technologies offer centralised services. Both technologies allow remote connections. Both technologies can enable the use of thin clients and present applications and data outside of the network. In a recent Brighttalk presentation that discussed VDI vs RDSH (VDI vs RDSH Balancing Security, Budget, Performance and Mobility) Mike Fodor from Teradici discussed four key business requirements factors to consider when architecting your solution.
- Application Diversity: More diversity of an application estate favors using VDI. If your business has users who have complex or demanding app environments, VDI is often the better choice. RDSH, on the other hand, favours uniformity. Everyone just pootling about with MS Office? Need to push out that database application?
- Application Compatibility: VDI gives you the option of delivering a desktop OS, which can reduce complexity for deployment. However, there are many applications where this is not a problem. It is difficult to segregate applications without adding more servers in an RDSH environment without using application virtualization; still, an RDS Client Access License entitles you to use App-V in your RDSH environment.
- Cost Factors: While VDI can be the more flexible in terms of providing an instance for a user, it is typically more expensive than RDSH to license, and to support in terms of hardware. VDI must have a hypervisor, RDSH need not have a hypervisor. While the hypervisor for VDI is often free, it still needs to be managed and maintained. That said, RDSH needs a server OS license.
Bear in mind VDI security is not better than physical desktops. While it could be said VDI often is used to allow users to be admins and RDSH tends to be locked down, that doesn’t make one more secure than the other. There is a potential risk in both environments. Reducing the attack possibility of the endpoint by making it a zero client is one consideration in a range of measures that look at permissions, network access, features, logging, and control.
It also used to be that demands of user experience and bandwidth drove a particular choice: RDSH was serviced by Citrix’s HDX/ICA, Ericom’s Blaze, or Microsoft’s RDP. While VDI was also serviced by these protocols, in addition you had Teradici’s PCoIP. However, with Teradici’s release of their Arch Technology Preview, this too is no longer the case.
Ultimately, the hearts and minds of the business need to be won by listening to the business needs and working through a Proof of Concept environment for a range of users across the organisation. Different user populations can require different solutions. VDI and RDSH is not an “either-or” choice; many organisations are successfully choosing to run both.
Calm Down Dear, It’s Only a Desktop Deployment
Of the two desktop virtualization technologies, VDI can at first glance appear the more straightforward, but licensing and delivery is often simpler with RDSH. For PC desktop delivery, VDI does have a veneer of familiarity and a 1-1 mapping of user to instance. But, RDSH has a licensing model that scales beyond Microsoft-corporate-license-at-the-endpoint complexity.
If your virtual desktop infrastructure is to help push virtual desktops beyond 15-20% of corporate desktops, if your desktop virtualization solution is to help push out applications and data into your wider enterprise mobile and user-owned devices, then your solution likely needs both VDI and RDSH. To get the best value you need to sit both hosted desktops (VDI) and remote session hosts (RDSH/Presentation Virtualization/Terminal Services) down and rather than bang their heads together, get them to play nice.