I have been remiss in not commenting sooner on the usefulness of the Exchange 2010 Mailbox Server Role Requirements Calculator, an Excel spreadsheet that demonstrates the level of complexity that this application can reach. The current version of the calculator is V17.8 and it can be downloaded from TechNet. This sad failing on my part was brought home to me during a session on designing for disaster scenarios delivered by the redoubtable Ross Smith IV at the recent TEC 2011 EMEA conference in Frankfurt, Germany.
The calculator started life as a project to help Exchange administrators understand how much disk space they would require to accommodate all of the databases and transaction logs within a Database Availability Group (DAG). As you know, the DAG is a new high availability feature introduced in Exchange 2010 and like all new features, effort is required to explain the intricacies and potential pitfalls of the new technology. Ross Smith IV, a well-known member of the Exchange Customer Experience team who spends no little amount of his time explaining all about the DAG to customers at conferences such as TEC 2011 (see this blog post for an example of his insightful writing about the DAG), is the lead author for the calculator and has done a sterling job to keep on adding value to the spreadsheet.
The latest version includes the ability to visualize what happens when failures occur inside a DAG. Failures are a fact of IT life and come in many varieties. The ones that are of most concern to DAG designers are storage failures (single disks or arrays), mailbox server failures, and, at the high end, failures that render a complete datacenter inaccessible.
Events flow as a result of a failure. In the case of a DAG, you want to know how well the DAG will cope with the loss of a database, server, or datacenter. The calculator allows you to see how the databases within a DAG are best laid out to resist failure and then model what happens should servers begin to fail. Parameters can then be tweaked to ensure that the desired level of resilience and other factors are met. For example, you can add more servers or database copies to the mix or see what happens if a higher volume of message traffic has to be processed. You can change the type of disk to use to experiment with SAS vs. SATA vs. FC. You can determine that each database should only support a certain number of mailboxes, and so on. You can even model configurations based on virtualized servers.
The calculator also boasts the very useful feature of being able to export PowerShell scripts to configure everything for you after you’ve arrived at the optimum settings. These scripts are prototypes that have to be updated to meet the needs of an organization such as naming conventions but they make a very good starting point for the work that needs to be done to roll-out a well-configured DAG that matches the design arrived at through the calculator.
As always, tools like this cannot deliver the total answer because it is impossible for any software to capture all of the requirements and peculiarities of a company. However, the Mailbox Server Role Requirements Calculator is an excellent utility that should be in the toolbox of anyone who is setting out to design high availability server configurations for Exchange 2010. Recommended!