"I'm saying right now I need 80 terabytes but over the next three years we believe that will treble to a quarter of a petabyte and I expect to be buying on these schedules, which we have outlined. What I want from the vendor is the right to buy disk on a pre-negotiated price," he said. "They might say we are offering you this deal today and we are taking 30 per cent off our normal price. Most people would say that is fine.

"But I want to see is that price come down over time, as storage comes down over time. I want my 30 per cent discount but I want it 30 per cent discount to whatever that storage costs on the day. Or I want that price to decline 10 or 7 per cent per quarter. The idea is 12 quarters out I might be saving myself 30 per cent."

In short, you need to exploit the commodity curve and avoid having to pay too much upfront. There will always be other factors to take into account, but the key messages in this guide should always be kept in mind when buying a storage array: Conduct an audit of your data; consider undertaking a request for proposals; and negotiate to ensure you get a good deal that continues to pay off as your capacity requirements increase.