One of the (many) proverbs about data centres goes like this: the only thing more expensive than building a data centre is keeping it running for any length of time.

To maintain an enterprise’s core is expensive. As well as cooling, electricity, safety and security, there’s the bandwidth cost – both between data centres and between data centres and users. As long distances are typically involved, an entire industry sprang up devoted to saving communications bills by compressing data before it travelled over the WAN.