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In the world of desktop virtualization, there are two prevailing technologies: RDSH and VDI. They're based on similar principles, but RDSH has a much longer history and, perhaps, a longer future.
Until the mid-2000s, Remote Desktop Session Host (RDSH) was the only show in town, but the advent of virtualization and the possibility of isolating one user from another gave way to VDI. VDI is often the prevailing virtual desktop deployment mechanism today, but it has not replaced RDSH.
On the surface, VDI and RDSH are very similar. Users log into a device that connects them via a display remoting protocol to an application or a desktop running in a data center or the cloud. The differences become clear when you look at the server-side infrastructure. VDI provides a single virtual machine to each user, isolating that user and providing them with a unique desktop. RDSH most often shares a single instance of Windows Server with many users. There is less overhead with RDSH because the operating system bits and pieces don't need to be replicated for each user, but there are potential problems with users sharing a single pool of resources.
Where RDSH excels
IT can deploy Windows applications and Windows desktops via an RDSH process called publishing, which allows the administrator to assign an application or desktop to a user or group of users.
Deploying published applications presents only a single application to the user without a full desktop. In truth, the desktop is there, but it's hidden from the user so the only thing they interact with is the application itself and nothing else hosted on the same Remote Desktop Session Host server.
Deploying desktops to end users is pretty straightforward. Each user connects to the full, published desktop of the RDSH server. RDSH is almost exclusively talked about as an application virtualization product, but an enormous amount of RDSH organizations today connect to desktops. RDSH-based desktops on shared servers consume fewer resources, meaning IT can support more users for less time, resources and money.
Where RDSH falls short
With RDSH, there are dozens or even hundreds of users connecting to a single server. If even one of these users has privileges that would allow them to, say, delete an application or power down the server, that would affect all the other users.
There are also issues with application compatibility. Especially in smaller environments, the RDSH servers host all the applications that users need to access remotely. As the number of applications grows, the chance of one application stepping on the foot of another increases. The common way of dealing with this problem is to create server silos where each group of servers only contains a single application. Even with silos, however, IT has to test every update that comes out for each application to ensure that it doesn't break the other applications on the RDSH server.
Because of this extensive user-proofing and advanced application compatibility work, RDSH requires as much of a desktop and application skill set as it does a server and security skill set. With the right knowledge, Remote Desktop Session Host remains an excellent choice for hosting desktops and applications, but it's easy to see why VDI generated so much buzz. With VDI, you need some new infrastructure knowledge, but the day-to-day Windows management is nearly identical to what the desktop support team already does.
The future of RDSH
VDI is focused on delivering Windows desktops, but when the time comes that we rely less on the desktop, VDI will fall out of favor. That's when RDSH's stock will rise again.
The seeds of a Windows desktop-less future have been sown. More applications are moving to the cloud than ever before, and each one that does reduces the requirement that we run Windows to access them. As users' identities migrate toward the cloud, which is happening with Microsoft Office 365 and OneDrive, IT will rely less on Active Directory and other classic data center-based services.
There will be certain Windows applications that, for one reason or another, cannot be replaced. As long as those applications exist, IT will have to deliver Windows to end users as a way to run the application. In this desktop-less future, the go-to platform will once again be RDSH. We already see this today with legacy applications that can't run on modern operating systems.
Remote Desktop Session Host is like that old car in the garage. It's not as flashy as the neighbor's new ride, but it just keeps plugging away and doing its job. And long after the shine comes off the new car, that old one will still be there getting you from point A to point B. After all, desktop virtualization is a set of tools. If it gets the job done, who cares what it looks like?
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