Costs of building your own data center

There are other reasons to build your own, especially for those who aren't just running web sites.

One is security. Maybe you don't want to be on the internet, or are legally prohibited from being on the internet.

One is location. Maybe you need to process data at the south pole, or in a submarine, or in a space station. Latency might matter, making even normal parts of the USA be too far away. Your connection to the data center might be unreliable, with outages being equivalent to data center outages, so you'd want your data center local. An example is the Large Hadron Collider, which has a really high data rate.

One is atypical hardware. Maybe you need to run a custom accelerator chip. Even something as simple as SPARC or Itanium might have you running your own data center.

>Construction of a mid-sized Enterprise DC (just 5000sqft), at just "tier3" availability (3 9s) will cost around 40m. If you want 5 9s redundancy you will need 1-2 failovers, so 3x that. Incld racks, cooling, power, construction and land. Using a colo @Equinix will likely save 20%

I don't get the part about using Colo will only save 20%. You don't have to build a DC just because you don't want to use other's people cloud. Colo is an option, without much of the hassle. But the saving were only 20%?

It really depends.

At very large scale owning can be cheaper based on contracts with various vendors. That said it’s really hard to beat cloud vendors particularly with various discounts in place at anything short of cloud vendor scale.