Well - RAID is more or a traditional architecture solution than a cloud one. A cloud storage solution like Ceph provides redundancy across nodes, and I've even read that they strongly discourage the use of RAID. Still, the orange box is a homogenous architecture that can be used flexibly as a training and introduction tool - I've not heard anyone suggest you run it as your production cloud. If you go and spec a real cloud you'll find vendors will provide different configuration for designated storage and compute nodes.