The below video shows how you can start (very) small with Nutanix, and scale to 1 Million IOPS and beyond in a linear fashion, in one node, or one block (4 node) increments and enjoy linear scalability.

http://www.youtube.com/watch?v=B-RBDtKgQTo&feature=youtu.be

So next time your looking to buy storage, why not buy what you need today, and not what you might need in 3 or 5 years time, and scale incrementally as required without the need for controller head swaps, or throwing out any equipment.