Common VCDX Mistakes: R01: Customer Requires N+1

Over the years as a VCDX panellist, I began seeing a pattern of regular mistakes that candidates make either in the VCDX Application process or in the actual VCDX Defense. So I have decided to write some short posts highlighting different mistakes. As usual, these are my own thoughts, and may not be shared by other VCDX panellists. If you are interested in my thoughts, you can either subscribe to my blog or follow me on Twitter to keep an eye out for new posts.

For those of you whole aren’t familiar with the VCDX program, you can read more about it here: VMware Certified Design Expert .

Today I want to kick off with the following:

R01: Customer Requires N+1

I see this in about 90% of VCDX designs. This implies that the customer has specifically requested N+1 for each vSphere cluster. Why has the customer requested N+1? As an architect, you should be working with the customer to first understand their Availability requirements (SLA). Once you understand the customer’s Availability requirements, you can then make a decision on how many failures your infrastructure can tolerate before the Availability requirement can no longer be achieved. It’s at this point you can make the design decision on what N+x value you will need to design for.

If a customer specifies N+1 and then in another requirement requires 99.99% Availability, will N+1 be adequate to achieve 4 9’s? The Availability (SLA) requirement should be understood BEFORE an N+x value can be determined. Not the other way around.

Feel free to discuss in the comment section below.

  • Andy Smith

    Something also to consider is that availability during planned maintenance. You might end up with extra capacity to not put your environment at risk for upgrades and patching.

 
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