Re: Reinventing your own file system. Multiple times.
There are a variety of enterprise supported products that include SAN, NAS and REST or any combination of those interfaces. Rolling your own isn't necessary though admittedly it's probably more fun.
I work for Quantum and am a Scale Out Storage SE so of course I prefer a StorNext with Lattus-M combination for your single vendor tiered storage needs but there are other products on the market that provide similar functionality like Qumulo and I think EMC ViPR has all sorts of cool capabilities like this as well.