5th April 2016, Oracle announced arrival of Exadata X6-2. Overview of all its capabilities can be found HERE. Check DataSheet for list of hardware components and capacity of each X6-2 rack.
Sometimes, Oracle changes hardware specifications for its racks e.g X5-2 was released with 4TB HDD initially, but after few months the datasheet was modified and Oracle started delivering X5-2 with 8TB HDD in storage cells. So, it is advisable to check the datasheet before ordering it to make sure that what you will be getting eventually.