This week the following tweet caught my eye:

“@wonder_nerd Fictitious designs in a #VCDX defense have a failure rate of 90%. #VMwarePEX” < interesting statistic — Mark Snook (@VirtualSnook) February 8, 2014



Apparently Marc Brunstad (VCDX program manager) stated this fact during the PEX VCDX workshop. But what does this stat mean and to what level do you need to take this into regard when submitting your own design?

During my days as a panel member, I’ve seen only a handful of fictitious designs and although they were technically sound, the reasoning and defense were usually not that strong. Be aware that the VCDX program isn’t born into existence to find the best design ever. It determines if the candidate has aligned the technical functionality with the customers’ requirements, the constraints provided by the environment and the assumptions the team made about for example future workloads or organizational growth.

But does that mean that you shouldn’t use any fictitious element in your design? Are fictiticous elements inherently bad? I don’t think so. Speaking from own experience I made some adjustments to my design I submitted.

My submitted design was largely based on the environment that I worked on for a couple of years. At that time the customer used rack-based systems, my design contained a blade architecture. The reason why I changed this, as it allowed me to demonstrate my knowledge of the HA stack featured in vSphere 4.1. Some might argue that I deliberately made my design more complex, but I was comfortable enough to defend my choices and explain High Availability Primary and Secondary node interaction and how to mitigate risk.

More over it allowed me to demonstrate the pros and cons of such a design on various levels, such as the impact it had on operational processes, the influence on scalability and the alignment of availability policies to org-defined failure domains. Did I have these discussions in real life? Yes, with many other customers but just not with that specific customer that this design was based on.

And that’s why complete fictitious designs fail and why most reasoning is incomplete. The candidate only focused on the alignment of technical specs and workload. Not the “softer” side of things.

Arguing that this design element was just the wish of a customer just doesn’t cut it. Sure we all met customers that were strung on having that particular setting configured in the way they saw fit, but its your responsibility to explain to the panel which steps you took to inform the customer about the risk and potential impact that setting had. Try to explain which setting you would have used and why. Demonstrate your knowledge about feasible alternatives.

My recommendation to future candidates; when incorporating a specific fictitious design element in your design, make sure you had a conversation with a customer about that element once. You can easily align this with the main design and it helps to recollect the specifics during your defense.