So called data center clusters arise for a variety of reasons — beyond the Northwest, there’s a cluster in North Carolina and Northern Virginia, among other places. Facebook and Microsoft have told us they have about 50 criteria for selecting certain locations, including low cost and reliable power, aggressive tax incentives, the need for rural areas, the need for available water, a desire for fast deployment, and even the lemming effect (data center operators feel more comfortable going to where the others are).

The Northwest area — Oregon and Washington — also have cool climates so that the next-generation of data centers built in those regions can use outside air for cooling, which cuts down on their need for large air conditioners and thus reduces energy costs. GigaOM visited Facebook’s data center in Oregon last month and brought you this rare look of how the air flows and server rooms look.

The good news is that data centers — and servers — are getting increasingly energy efficient, as larger and larger data centers are being built. AMD just released one of the most low power servers available on the market for webscale computing, based on ARM architecture (which is more commonly used in low power cell phones). Internet companies are also increasingly looking at clean power as an important criteria and source when it comes to where they build data centers — Apple is building a huge solar farm at its data center in North Carolina.

But cities, and some analysts, are still worried about the affect of the growing power consumption of data centers in certain regions. The Northwest Power and Conservation Council wrote a cautious report on the subject recently (report here). Data centers also don’t directly contribute a whole lot of employment opportunities — around 50 to 60 people work full time in the largest of facilities.

For more on this subject check out:

• The ultimate geek road trip: North Carolina’s mega data center cluster
• 10 reasons Apple, Facebook & Google chose North Carolina for their mega data centers
• The story behind how Apple’s iCloud data center got built
• The controversial world of clean power and data centers
• A rare look inside Facebook’s Oregon data center [photos, video]

Related research and analysis from GigaOM Pro:
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