On top of those costs, Uptime suggests that you plan to spend another $300 per square foot of computer room floor. You could also factor in $190 per square foot of empty space; that is, space set aside for a UPS system when your current system reaches maximum use.
The paper provides an example to illustrate how much of an impact moving from Tier II to Tier IV can make. A 20,000 square foot Tier II facility with 666 racks at 1.5 kW per rack (1,000 kW of UPS for your hardware) would cost a projected $18.5 million. If you sought to make this 20,000 square foot space a Tier IV fault-tolerant facility, you'd have 666 racks at 3kW per rack (2,000 kW of UPS for your machines), which would cost a projected $56 million.
If the differences in these capital expenses don’t give you cause to reconsider your Tier choice for a future datacenter, the differences in operating costs might. A higher-tier datacenter with more active, redundant power means you're paying more for power and cooling per server.
How much more? I've thrown out these figures before, but they warrant repeating. According to the Uptime Institute, powering and cooling a mid-tier, $2,500 server in a Tier II datacenter costs about $1,320 per year (including electricity, facilities operations, and facilities depreciation). In a Tier III facility, the annual cost jumps to $1,870. For Tier IV, it's $2,020.
So let's go back to our scenario and say that a company is putting twelve $2,500 servers in each one of its 666 racks. In a Tier II facility, the company would be paying approximately $10,549,440 per year to cool and operate its 7,992 servers. In a Tier III facility, the annual server operating costs are $14,945,040. And at Tier IV, you're looking at an annual tab of $16,143,840. Notably, as energy prices increase, so do these figures.
The lesson? It's critical to invest in IT equipment and facilities based on your actual needs; too many resources, including space, dollars, and electricity, are squandered on excess servers, storage, cooling, and such. Yes, there's something to be said for wiggle room and peace of mind, but there comes a point when the price of that peace of mind simply can't be justified.
The Uptime Institute's "Cost Model: Dollars per kW plus Dollars per Square Foot of Computer Floor" white paper is available for free here. I strongly recommend that you download it and read it carefully if there's a datacenter project on your horizon.