Hosted Shared "RDP" Desktops vs true Virtual Desktops
A discussion on virtual desktop infrastructure Technologies
A lot of people think that Remote Desktop Services (Microsoft) and Citrix XenApp/RDS are true Virtual Desktops. Although the desktop operating system may be on a VM (virtual machine) on the host machine, that is only the server virtualization aspect.
True "Virtual Desktops" involve connecting a remote display unit to an isolated desktop operating system (like Windows 7) contained in ('executing in') in a Virtual Machine (VM) running on a separate physical VM host machine. This host machine normally runs numerous desktop VMs.
The "Hosted Shared" (MS Remote Desktop Services or Citrix XenApp/RDS) model involves using a shared or multi-tenant desktop running a Windows Server. The desktop is that of the host server operating system like Windows server 2008 or 2012. While the user's desktop may look like a typical windows desktop, they are not, although users are seldom the wiser.
Which is better?
This is a more difficult question to answer.
From a technical standpoint, one drawback with shared model is that a fault that requires a restart will affect all desktops running on that server. In practice, this is fairly rare.
Some software vendors may claim that their applications that are written for Windows desktop operating systems and not Microsoft server operating systems. In the early days this may have been an issue, but since MS Server 2000, we rarely see any issues.
In the true VDI model, each desktop is isolated, so if a user has some fault, all it takes is a restart of the individual desktop not the entire environment. The desktop, furthermore, is provisioned from a master tested image which affords the ability to regenerate completely new desktops, about a 20 minute process in our experience. That said, the VDI model is far more resource intensive than RDS (Remote Desktop Services) or XenApp/RDS. This is easy to understand as each user gets their own virtual copy of the full Windows 7 or 8 operating system in their private virtual container.
In the VDI model, in order achieve a modicum of performance, one needs about 40% more in memory and significantly higher CPU speeds and cores than for the shared model. The disk space required is about 3 times as much and one needed to be extremely careful as to where and on what types of drives the user desktops and data were placed. The "thin" part of the bandwidth needed between client and server, furthermore, is well, not so thin for the VDI model. That is because under VDI, we are remoting true and full desktops. That may be fine on today's 1gB LAN segments, but on the WAN, performance seen by the end user can be challenged by the speed of their local internet pipe.
Fortunately, as VDI gains in popularity, more vendors are developing technologies for the client-server connection that optimized the end user experience. The technical details are beyond the scope of this discussion.
In the end it comes down to budget. For small environments, the licensing and hardware costs of true VDI will present a challenge to small and medium organizations' budgets. While we like in Citrix's XenDesktop and to limited extent their VIAB (VDI-in-a-Box) grid architecture, in order to get redundancy and performance, one would need a substantial investment. As you grow and scale the VDI model , it requires more servers as compared to the hosted shared desktop model.
Most small organizations, let's say under 100 (perhaps even under 500) would find the cost of true VDI cost prohibitive compared to that of RDS or XenApp/RDS. Both technologies moreover, deliver nearly the same benefits such as reduced I.T. support costs, higher reliability and universal remote access from a wide array of devices.
For larger environments, the infrastructure required for the shared model could approach that of VDI solution if the licensing costs from Microsoft were decreased and VDI vendors further optimized their software.
In conclusion, we believe that currently, small and medium organizations will be better off with Microsoft RDS or Citrix XenApp/RDS.
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