It's unlikely for cloud hosting that you would want to use NAS. You would be better off with SAN, so as other posters have said Ceph (a building block of OpenStack) is a very good choice.
High Performance, Low Contention, Hosting
Elastic Sites (HIgh Powered Hosting Accounts) with 1 to 20 CPU Cores, 4 to 42GB of RAM. (Power of a VPS without the hassle)
Shared, Reseller, VPS, Dedicated & More available