Microsoft has worked hard over the years to simplify the installation and configuration of their software... Next-Next-Finish - Job done, server is working, the boss is happy. Microsoft has also worked hard to provide supporting documentation and tools to assist with the design of systems. That's what I'm going to talk about here...
There's a great article from Neil Hobson, an Exchange MVP, on the sizing of Exchange solutions which pulls together a number of these tools to analyse, calculate, plan, design, stress-test, load-test and finalise your system design. Hundreds and hundreds of pages of technical documentation is available for download if you want it.
What's most worrisome though is the massive possible variance in the results from these tools – first up, you need to estimate the profile of your users; light, average or heavy-user, based on the number and size of emails they typically send. Some wrong numbers here or some increases in mail usage can throw those results out of the window. Why do I say this? Because we know how easy it is to get this wrong. Take a look at the article – have you got you CPU-core and storage group ratios right for the RAM you have in your servers?
Capacity planning, which includes performance planning too as an over-capacity platform equals performance issues for sure, is the biggest single challenge for any hosting company. If you don't get this right it goes very wrong, very quickly. My teams spend a lot of time working with these tools modelling and re-modelling our system designs using actual production user profile data, and despite our best efforts the resulting designs vary in more ways that you'd imagine. We overcome this issue with an N+1 model for redundancy with an additional +1 added for capacity, i.e. we always have at least 1 more server or cluster than we need in the already redundant solution.
Using a hosted service completely removes the unpredictability of capacity management. There are no issues with increasing or decreasing user numbers, no worries about the impact of increased usage profiles, more traffic, email volumes or variables which are out of your control.
So don't read those documents and don't download the storage stressing tools – you don't need the stress!
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