People designing Exchange storage layouts often use the excellent Microsoft Exchange storage calculator. This is a great first step, but the tool does not include a couple important things. One is background database maintenance (BDM) which can sometimes cause a disk IO testing tool like JetStress to fail. Another is that it lacks in providing a visual view of the Exchange layout.
EMC’s extensions add in some of the IOPS details (like BDM) that the base calculator might miss and we’ve also designed a tool called the DAG Instant Visualization Application (DIVA) that helps to visualize the environment in a more legible way. Watch this great video interview with Jim Cordes (creator of these tools) for more details!
To get the calculator with EMC extensions and DIVA, go to the Everything Microsoft site.
[updated 2/1/2013] Here is a link to a recent training module for this calculator.