In the past I've written that VDI is "just a single user terminal server." But I've also written that one of the ways VDI projects fail is "thinking VDI is nothing more than a single user terminal server." Obviously these two statements are at odds with each other, so what gives?
To understand the discrepancy, we have to dig into the differences between Terminal Server/RDSH-based (Citrix XenApp, etc.) and VDI-based (Citrix XenDesktop, VMware View, etc.) projects. I'll use Citrix's product names in this article, but the concepts apply to any RDSH and VDI environments.
Because there are over 100 million Citrix XenApp users in the world, and the product has been around in one form or another for over fifteen years, many of us have confidence that "we know how to do HDX, we know how to do thin clients, etc." The knowledge we have is based on HDX and thin clients for XenApp. Most companies use XenApp either to (1) deliver a few corporate apps to users with existing desktops and laptops, or (2) deliver a complete desktop via a thin client to so-called "task workers" (call centers, shared terminals, etc.).
But when it comes to VDI, even though the HDX protocol and the concept of thin clients are the same as with XenApp, the use cases are wildly different. For example, users who only use XenApp for a few applications do their "heavy" work (web browsing, graphics, peripherals, etc.) via local applications running on their desktops. XenApp-based task workers with thin clients don't push XenApp and HDX to its limits.
But when it comes to VDI, it's more of an "all or nothing" thing for users. Companies don't use VDI to augment existing physical desktops—they use VDI to replace existing physical desktops. (After all, if you can't replace the local desktop, then adding VDI just means you're managing two desktops per user instead of one.) But the fact that VDI is desktop replacement this means that your HDX (or PCoIP, RDP, RemoteFX...) connection has to support everything that users want to do—web browsing, audio, video, peripherals, 1900x1080 resolutions, multiple displays, client side cameras and microphones, finger print scanners, etc.
Unfortunately companies quickly learn that the networks, protocols, and thin client devices that work fine for "just a little XenApp here and there" break down when companies try to use them with the power and capabilities required for day-in, day-out heavy desktop VDI usage.
"Everyone who needs a thin client is already using one"
When VDI first came on the market a few years ago, the thin client vendors started making devices that were specifically tuned to VDI use cases. I scoffed at these, writing that "everyone who needs a thin client already has one."
Yet despite my skepticism, thin client (or smart client, zero client, cloud client, whatever-they-call-it client) sales grew, and both Wyse and NComputing had their best quarters ever in 2012. (HP might have too—I just don't have that data.)
So again, what gives?
This is when I realized that the thin clients people were buying were for VDI and desktop replacement projects. For any existing XenApp projects, yeah, everyone bought that hardware five years ago and it still works fine. But the people who are using VDI have chosen it over XenApp because they have some specific advanced need—they're doing that desktop replacement or that advanced powerful application or something like that. And in their cases, the thin client device from five years ago just won't cut it. They need dual displays and USB2 and client side audio and the ability to plug in phones and cameras. (In a sense, they need a desktop!)
By the way, it's also interesting that the thin client devices sold for today's desktop remoting are not necessarily more expensive. Sure, they have more capabilities to satisfy the requirements of the full desktop VDI-based remoting, but in terms of cost, HP, Dell/Wyse, and NComputing all have HDX-capable devices starting under $200, and for $300 you can get something that supports multiple 1900x1080 displays.The bottom line is that people go to VDI because they want datacenter-based desktops to do things that RDSH and XenApp can't do, and that requires a different thin client than what they purchased in the past. But fortunately those thin clients are available today, and they're selling like crazy!