Exchange 2010 has a new I/O pattern that results in 70 percent lower I/O requirements than Exchange 2007 (and Exchange 2007 had 70 percent lower I/O requirements than Exchange 2003!). This reduced I/O pattern, thanks to optimizations that make it so writes don't come in bursts anymore, combined with advancements in SATA drives, means SATA is now a realistic storage platform for Exchange 2010. SATA was previously just for desktop systems.
Microsoft recommends when using SATA storage you have your mailboxes replicated to at least 3 other servers in your organisation using DAGs - the latest and greatest in exchange mailbox high availability... see:
Mailbox databases are replicated and are made highly available with load balancing accross your organisation, no server becomes mission critical. When deployed correctly if a single mailbox server was to fail, no one would care... where with previous versions people would be panicing. The server can simply be repaired whenever the administrator gets a chance... 3 months down the line if need be.
Also as long as you have your mailboxes replicated to at least 3 servers Microsoft says you no longer need to worry about backing up to expensive tape devices and storage mediums. This also comes about with the new Dumpster 2.0 replacing the old Dumpster 1.0 that was used in exchange 2003 and 2007. If you need all mail to be kept for 10 years, even after a user has deleted it, you can configure this using the dumpster allowing administrators to manually recieve deleted items from the DAG on any physical server. Quoted from Microsoft "Your organization can rely on the Exchange 2010 high availability infrastructure—which can provide up to sixteen replicated database copies—rather than tape backups to recover from failures, which helps you to reduce operating costs."
For more about dumpster 2.0 read:
Because SATA is a cheap storage solution where you can buy 2TB drives for next to nothing these disks will be locally attached to the servers. My recommendation is to not virtualize the mailbox servers as they ususally have high load even in a load balanced solution. This is one of very few servers in a windows environment I would not virtualize, nearly everything else should be virtualized. Microsoft does not recommend virtualizing servers with high utilization!