Tonight I’ve been reading an article about data center building trends. There’s some very good points to this and also some things that I think are very wrong. These also explain some things that have mystified me for some time.
Looking ahead 5 years for capacity planning isn’t a bad idea (except that the data center needs to be flexible enough to accommodate the changes that can happen in 5 years), but the whole decision on build out or not for data center infrastructure in advance hinges on the penalty for doing so. In short, there’s no penalty for building out passive infrastructure and a big penalty for building out active infrastructure.
I’ve been mystified by the idea that data center PUE (power usage effectiveness) only gets good when a data center is full. Now I understand, this is based on the idea of a data center building out (and operating) 100% of it’s cooling infrastructure in advance. If you’re only running 20% of your 5 year forecasted server capacity but you have to run 100% of your 5 year forecasted cooling capacity because it’s a monolithic system that’s either on or off, of course your efficiency is going to stink!
The PUE numbers for that kind of arrangement would be pathetic. Of course, as you add servers with the same amount of cooling power usage, the PUE would gradually get better, but who in the world would really WANT to run something that way? (Reference last year’s story about UPS cutting their data center power by switching off 30 out of 65 HVAC units!)
Leaving plenty of extra room for the transformer yard and the generator yard is a great idea (you can’t expand them once you get things built in around them). On the other hand, it would be silly to build out and power up a yard full of transformers that were sitting there doing nothing except chewing up power.
So, what sort of data center infrastructure things can safely be built out far ahead of the actual need? The physical building is a bit of a no-brainer, as long as the active sections can be isolated from the idle (you don’t need to be cooling an entire hall that’s only 10% full).
Passive electrical is another good one. This means entrances, disconnects, breaker panels, distribution cabling, transfer switches. No UPS, no DC power plants unless you’re going to be able to shut them off and leave them off until you really need them.
Passive cooling infrastructure such as ducts. Take a lesson from UPS, do NOT build out double the HVAC you need and run it all!
Finally, build out the support structures for the transformer and generator yards. Mounting pads, conduit, cabling, so the equipment is all set to drop, hook up, and go.
Don’t kill your data center’s efficiency in return for capacity 5 years from now.
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