For those of you with OSE Tribe access (limited to EMC Employees, unfortunately), Kevin Closson has created a two part series of videos entitled:
If you have not seen these videos, trust me, you definitely want to see them. They are fabulous. They will eventually be posted on this site as well.
The basic idea behind the videos is that ExaData has many performance bottlenecks that waste resources and limit performance. Please comment here on your experience with this.