This is a pet topic of mine because I believe that the world has never realized the potential of Terminal Server, or Session Host as it is now called. And the thing that really stuns me is how many times departments running VDI pilots are trying to make the economics of VDI work and they have never heard of Session Host, which is typically one quarter of the price, and uses much of the same “thin client” or “remote desktop” technology.
First, a quick terminology check – by “VDI” I mean Windows XP/Vista/7 running as guest VMs on a hypervisor and accessed remotely from thin client hardware or software. By “Session Host” I’m referring to a Windows Server hosting multiple user sessions, also accessed with thin client hardware or software. In my opinion, both are forms of “desktop virtualization”, but I’m saving that argument for the next post.
For all its greatness, there are situations where Session Host just won’t cut it, so here are my top eight reasons why you might choose VDI when virtualizing and hosting your Windows desktops and apps. Of course, to achieve the lowest average cost per user you should really consider a blended approach: Session Host for task workers, VDI for advanced users.
- Application Compatibility and App Vendor Support
Some apps are hard to make work on Session Host without clever redirection technology and compatibility shims. One of my colleagues proudly boasts that there have only ever been about 5 apps he couldn’t get working, but he’s an MVP. You can get 95% working with a mere mortal. And a much bigger problem is that even when you get it working you might find the app vendor won’t touch it unless it’s running on XP/Vista/Win 7.
This is probably VDI’s single biggest advantage over Session Host. In a nutshell, most apps will just work in VDI. Not all – some need specific hardware, some consume too many resources, but in general most do. And when you phone Technical Support for your poorly-supported third party application and they ask what platform it’s running on you can say “XP” or “Windows 7” with confidence rather than a nervous “Windows Server 2003 Terminal Server” followed by “click … buzzzzzzzzzzz” as they hang up.
Does this justify the massive price hike over Session Host because of the lower user density and higher licensing costs? That’s where ROI models are needed. And before someone says “Moore’s law” and “the price of VDI will come down” – if you can put twice as many VMs on a server, you can put twice as many sessions on that server running as a Session Host.
. - USB Device support
If you have to work with a specific device, USB redirection technology is available for VDI so it will work with your remote desktop and applications. Doing the same on Session Host is near impossible without every other user seeing that device, and destabilizing every other user as the device driver loads. I’m not talking standard USB keyboards and mice here, which work just fine in Session Host. You can also use USB printers and headsets if you use the remote printing and 2-way audio technology available for Session Host. No, the issue here is with things like media devices and specialist scanners which require specific device drivers to work.
. - I have to reboot my desktop 4 times a day
The shameful truth of many organizations is their business is totally dependent on old, unsupported apps that leak memory like a sieve and take down the whole PC quite regularly. You can’t reboot an individual session in Session Host, but you can reboot a VM.
. - Advanced Graphics Requirements
Teradici’s PCoIP and HP’s RGS are two remote display protocols available on VDI and blades, but not Session Host. They use the bandwidth available on a LAN to deliver many frames per second and a rich experience to powerful devices, especially those with hardware acceleration. The bandwidth requirements seriously limit their suitability for branch office (WAN) and remote users, but when you have bandwidth and money to spend on expensive access devices they work very well.
Microsoft’s forthcoming answer is RemoteFX, which is coming soon to both Session Host and VDI, although it will have some features (virtualization of GPU hardware) only for VDI. But for anyone not doing 3D animation, Session Host can deliver a rich experience just fine thanks, especially with the forthcoming RemoteFX ASIC encoders which should be cheap since the license to build the chips is royalty-free.
. - Physical to Virtual Migrations
If you’re really going to virtualize your existing physical desktops then (a) VDI is the only way to go, and (b) open your wallet for a gigantic NAS/SAN because you’re going to be using persistent desktops as opposed to pooled ones. Virtualizing your desktops is a great time to start again and clean up your desktop and application estate and consider pooled desktops, but with P2V into VDI it is completely possible to migrate the old ones into the datacenter and keep right on going if you can afford the storage.
. - User-installed Applications
Users cannot install their own apps on Session Host, unless you want them available to all other users. One possible workaround is that they can self-serve packaged virtual apps and stream them into their session with something like App-V. VDI with persistent virtual desktops does offer a way to support user-installed apps, but it’s by far the most expensive form of desktop virtualization and many VDI pilots are now using non-persistent (aka pooled) desktops together with app streaming, virtual user profiles and redirection of user data to file servers to reduce storage costs. One possible solution here is emerging with new products that allow user-installed apps to be used on non-persistent desktops with “layering” technologies, but they have limitations on the types of apps they support.
My personal feeling is that if you really want your users installing apps themselves, give them a PC and give them their business apps in a secure, contained, virtual environment inside that PC. Of course, they’ll still break it, but it should be faster for them to get productive again since they can use any other computing device available to get to their business apps. If you really want to reduce desktop TCO, you need to restrict your users. VDI doesn’t change much here. If you let them install their own apps, they will break desktops whether they are virtual or physical. Virtual ones are just faster to recover.
. - Application Features which are not available on a Session Host
Some apps, notably Outlook, disable certain features on Session Host, notably Search. This is because it’s a resource hog and only suitable for use on a dedicated computer. That makes it unsuitable for VDI too, but some people insist on trying. Again, break out that wallet for lots of fast storage and low user density on your VM hosts if you want to enable these kinds of features under VDI.
. - Business Continuity
I left this till last because although it’s touted as an advantage of VDI, and there are lots of evaluators who insisted they would use VMotion/Live Migrate, I’ve never actually heard of it being done in production. Please correct me if you are! The theory is that a live desktop can be moved to a different host to allow maintenance on the first host. In practice, many deployments use non-persistent desktops anyway, so users can just logoff and log back on and get brokered to a new host, and it requires a lot less hardware and resource than VMotion/Live Migrate which is better suited to virtualized servers than desktops.
Summary
VDI has a number of advantages over Session Host as a desktop virtualization platform, but they come at a price. Finally, forgive me one little plug – at Quest we don’t mind which way you go, or whether you blend the two techniques. Quest vWorkspace lets you manage both Session Host and VDI from one console, one set of policies, one broker, one remote client. Sweet. www.quest.com/vworkspace
