If you are thinking about designing any system that you wish to be reliable and resilient, then I suggest you read this great article;

http://blogs.technet.com/b/trustworthycomputing/archive/2013/05/31/improve-the-reliability-of-your-service-with-resilience-modeling-amp-analysis.aspx

This could be applied to an Exchange, SharePoint or any other application deployment, not to mention of course, private cloud.

Mark Sewell - UK PFE