Hello,
Last week i passed my VDCD550 exam and got VCAP5-DCD certification, so i guess i have some experience to share.
Last few years i worked at PM/management positions at various integrators but recently decided to go more technical again. So i updated my VCP4 to VCP5 in february and was ready to study for VCAP exams. I decided to go with VCAP-DCD, as, to be honest, i didn't have much hand-on implementation/administration expirience last few years. On other hand, i have pre-saled and designed some environments, so choose design path was obvious decision.
My studing materials were:
VMware vSphere 5.1 Clustering Deepdive by Duncan Epping & Frank Denneman
Managing and Optimizing VMware vSphere Deployments by Sean Crookston and Harley Stagner
- vSphere Design Pocketbook eBook by Frank Dennenman
- My notes from VCP5 preparations (lifehack: i use Microsoft OneNote for various work and personal life related notes and it just awesome, it has really nice Windows desktop app, plus it stores data in the cloud, so you can always use mobile apps to check on content and alter it a little bit, if necessary)
- Articles and white papers from exam blueprint
- Great series of "Architectural Decisions" posts by Josh Odgers http://www.joshodgers.com/architectural-decisions/
It was obviously overkill, as you don't need so much data to pass exam (and to be honest, deep technical knowledge isn't needed to pass it), but as i plan to pursue this field of work futher (and may be even continue to VCDX certification), more knowledge won't hurt.
When studying it's better to pay close attention to definitions of requirements, assumptions, constraints, risks and differences between them. Sometimes they are close to each other and phrasing matters very much. Good thing to do is review design you have previously completed at work and write down requirements, assumptions, constraints and risks.
Another point to pay attention to is how exactly are example designs in VMware documentation drawn, something like that will be expected from you. For example, during my exam there was one design 'visio like' question about storage. I've drawn all the objects and almost all connections and then was stuck with ALUA optimized/unoptimized paths. I mean i knew how it would work in real life but i just couldn't figure out how design tool was expecting me to draw it. Design tool kept on giving me error message that i cannot use this connector this way.
Critical skill for this exam is ability to map customers words and wishes to specific features and configurations. Descriptions might sound very unspecific and sometimes even cryptic, but hey, in real world customer very rarely give you structured and well-thought requirents either.
Apart from reading, it's very useful to complete some designs just to arrange your mind in proper way 
I used this:
- Review of previously completed customer desings. Try to use same approach as Josh Odgers in previously mentioned article series: determine requirements, justify your decision, think about alternatives.
- Paul McSharry's practice DCD scenarios: http://www.elasticsky.co.uk/practice-questions/. Use same approach.
- On-line practice exam http://www.virtualtiers.net This tool is absolutely fantastic, as it gives you look and feel of actual exam. It considerably lowered my stress level
Prepartions took about 1,5 months and i thought i was ready.
Now to the exam itself. First, there is no test center certified for VCAP exams in my town, so i had to wake up at 4:00 in the morning and drive 5 hours to certified test center. On the bright side i had additional 30 minutes to exam time, as i live in Russia there is time bonus for non-native English speakers.
So, it was 42 questions and 4 hours to go for me. And it's when funny thing happened. I either misread exam description or it was written incorrectly (though i guess it was the first ), but at that point i was sure, that after that 42 questions i will have another 8 design question and exam description strongly recommended to reserve at least 2 hours and 15 minutes for those 8 questions. In fast, those 8 questions was included in total exam question count.
As you see, at the moment it seemed to me i had to complete 42 questions in less than 2 hours and then take hardest part of exam. Luckily i was wrong, but as i've seen clock ticking, i became more and more nervous. Due to that i didn't gave some of the questions much thought (maybe for the better, as overthingking something sometimes worse then underthinking). Anyway, i was done with 42 questions,there was still hour and half left, and, to my (very pleasant!) surprise it was all, i passed with 346 score. Well, it may have been higher, if not my description reading mistake, but a pass is a pass.
To summ it up:
- Know requirements, assumptions, constraints and risks. Practice determining them from practice tasks and real world situations.
- Know differences between conceptual, logical and physical design
- Know how logical and physical design diagrams should be drawn from VMware point of view
- Try to think as an architect, always justify your design decisions, think about possible alternatives
- Design some enviroments (even completely imaginary), or review designs you did at work. View this as a little mind game for spare time, if you have to sit in the car and wait 15 minutes for your girlfriend - why not design a cluster meanwhile?
Hope it helps.
As for me, i'm now studying NSX and it's definitely amazing piece of tech. When VCIX6-DCV will be available, i'll try to pass implementation exam and yearn this certification.
