To work this out we need to start from first principles, way back in 2005ish.  We had many expensively maintained fat desktops, spare CPU cycles in the data center and a virtualisation layer.  This meant that we could take the fat desktops not already covered by terminal server (which only counted for around 20%) and move them into the data-center.  These new desktops would allow our users to install apps, personalise their OS, and IT could keep the environment stable.  People were saying things like ‘I can give my users local admin privileges!’.

That was the dream and it all sounded pretty good.  Then people realised that they would have to change cheap storage on the end point for expensive storage in the data-center.  Also it just seemed, well silly, to have 5000 copies of explorer.exe sitting on the SAN.  The advantages of data de-dupe were talked about, but the model that everyone settled on was a golden OS image, Citrix had Provisioning Server and VMware had linked clones.  Not only did this solve the high SAN demands, it enabled us to only update/patch one golden image and it worked for everyone! Double win!

So now we have thousands of users on one golden image, trouble is we need different application sets.  No Problem! said the industry, we have application virtualisation, it’s even a fairly mature technology, ThinApp, Citrix Streaming, App-V and all the rest.  Except not all applications are suitable for streaming, some have license requirements that rely on MAC addresses, some install drivers or services, etc. etc.

In any large organisation there are maybe 2% of these applications which are generally more than 10 years old, but that can’t be dumped.  Out of say six hundred apps that’s only twelve apps that need to be in the golden image, so we increase the number of golden images to twelve, and the rest of the applications are streamed.

So far so good, although with this golden image model, we have hit a snag, to allow users to install applications, we need to use block level deltas to save the personal information.  Over time these block level deltas can grow to the size of the original installation, ruining our nice SAN space saving ideas!  Not only that, when you update the base image you can’t reconcile the deltas, you have to throw them away.  That’s no good, you can’t give users a facility and then randomly remove their changes.  OK, lets lock down the OS, we can use a profile solution to save user personalisation using the file system (although obviously no user installed apps).  For a great explanation of block vs file see Brian Madden’s post “Atlantis Computing hopes to solve the “file-based” versus “block-based” VDI disk image challenge ”

Lots of vendors already in the Terminal Server space, immediately said ‘We have a profile solution!’ and Appsense, RES, RTO, Tricerat etc put out VDI profile solutions.

All of this worked great in the POCs and pilots, trouble is when it scaled up to 1000s of users we found that the power users who were moving gigs of VMDK’s around or working with large media files etc. meant we had to have REALLY expensive Tier 1 storage at the SAN, it became uneconomical to move those users to VDI so we left them on their fat desktops.

So where does that leave us on our big VDI project?

• Multiple users on an OS image
• Application silos
• Locked down desktops
• Profile solutions from Appsense, RTO, RES etc.
• Users limited to Task and knowledge workers
• Oh yeah, print solutions from Citrix and ThinPrint.
• Desktops accessed via RDP or ICA

I mean what does that sound like to you?  To me it sounds EXACTLY like Terminal Server.  What we have done is taken a VDI dream and apply terminal server thinking to it, unsurprisingly, it’s now looking just like terminal server, but with extra licensing costs.

We need to apply some brand new thinking, there are vendors out there trying to do this, like the afore mentioned Atlantis, but before VDI really takes off we need to rethink a lot of things or Gartners prediction of VDI being a $65 billion business with 40% of the worlds professional desktops seems to be a long way off.