[keep320909]

I would go with two approaches. One in-cloud backup, maybe the same provider (to save traffic, but under different account).

Second low-tech offline onsite backup. You do not even need large server to plug all hdds at once, just swap harddrives like CDs or VHS tapes...

[ocius]

We're expecting the amount of data to double every year for the next couple of years. That would require a lot of storage hardware and maintenance cost, don't you think?