Explosive data growth is a big pain for every IT manager on earth. Many enterprises have their global infrastructures scattered among two or three continents. Maintaining file servers or filers all around the world isn't a simple matter: some of them are unattended, there are security concerns, backup/archive policies can't be complied with and on, and on.
Enterprises are figuring out how to consolidate this stuff while keeping a 24X7 worldwide service and, on the other hand, vendors are trying to address these needs, but few products turn into really usable solutions and the price can't fit every budget.
Recently I wrote about an interesting product from HDS and I'm sure you can list it on top of your possible choices for these kind of projects, but two drawbacks might keep them at a distance: the cost of the project and the feeling of being locked-in to a traditional block storage when you need to scale up on a single instance.
I'm sure you already know of Scality, a small French startup already mentioned on The Register, and its RING technology. To quickly recap, its product is software, normally spread across many nodes, built to deliver an object storage infrastructure.
It was developed with internet and service providers in mind and uses commodity x86 hardware equipped with off-the-shelf disks. Indeed, the principal Scality customers are ISPs (in Italy it recently closed deals with Tiscali and SeeWeb) ,which will use these infrastructures for internal mail storage and to sell object storage services like Amazon S3.
Scality's solution can cost half that of a traditional storage, with resiliency and scalability advantages, but the other side of the coin is that it hasn't a native CIFS/NFS gateway; you must access it via standard APIs (C or HTTP REST).
The only way to solve this issue is to adopt a supported NAS Gateway supported NAS gateway like the one from Nasuni, another small startup. The Nasuni filer is a virtual appliance - you can install it on a VM - acting as a local file server/cache for the remote site while dealing with data to-from the central Scality RING.
This odd couple allows great savings and, theoretically, solves the big migration path problem from a traditional storage infrastructure to global private cloud storage.
Obviously this is just conjecture because these two are small startups and big enterprises are always sceptical of working with such beasts; guess how they will react when you propose a project with two of them!
But the idea is good and surely needs further investigation to better understand how these products may work together when developing a real single, big, secure, multi-tenant private cloud