HP Storage Planning Calculator
Usually, when I need to size the storage for an Exchange 2007 solution, I use the Exchange 2007 Mailbox Server Role Storage Requirements Calculator spreadsheet, provided by Microsoft.
But there are other alternatives, such as the tool I'm going to talk about (I already blogged about it in the past).
HP Storage Planning Calculator for Microsoft Exchange Server 2007 is a tool provided by HP that helps you calculate the storage needs for an Exchange 2007 solution, based on some input parameters you must provide. If you use components from this vendor, the tool adjusts the output to the type of hardware you're using and can also you give you cost analysis.
"Based on a selected user (workload) profile; this tool calculates the number of hard drives (spindles); storage controllers; enclosures required to meet both performance and capacity requirements for the total user population. The tool is designed to allow for a variety of what-if scenarios and pricing; comparing RAID levels; hard drives (spindles) sizes; storage array controllers; enclosures; backup methodology/topology; tape drives; comparing Outlook client modes; and high availability options Cluster Continuous Replication (CCR) versus Local Continuous Replication(LCR)."