Load- and StressTest during and after PoC
VDI is a complex matter, not just due to performance, but complex in many ways (as can be read in the comments). But the basics are equals as with Server Based Computer (SBC) as we've been doing for the last ten years.
Durint the design phase you should always consider the capacity, and therefore the scaling requirements and possibilities.The impact of booting a machine is huge and logging in a user is about 150% of a regular user (as a guideline). Jim Moyle wrote an excellent article about IOPS in an VDI environment which I highly recommend : http://www.jimmoyle.com/2011/05/windows-7-iops-for-vdi-deep-dive/
The thing is though, you should always test the performance during and after a PoC (or in the development phase). What is the impact of one machine, one user or certain processes? What happens if you increase the users? What happens if all users write their billable hours at the same time?
This is why a LoadTest is key for success. A StressTest would have prevented the problems described in the article, or atleast you would have known upfront (and could have informed the managent before the managers started complaining).
I wrote an two part article about LoadTest / StressTest best practices here http://www.ingmarverheij.com/2011/05/loadtesting-best-practices-part-1/.
LoadTesting is relative easy and cheap if you know what your objectices are. If you have the chance, and I bet there is, make sure you can validate your design (and a bonus, you'll be able to see the impact of changes in the infrastructure or applications).
Biting the hand that feeds IT
