Following on from my previous entry I’ve recently read that Google have lifted the veil of secrecy on their data centres and are now showing the world how they make their DC’s highly efficient. They too, have opted for the decentralised Uninterruptible Power Supply. Well, actually it’s more than that. They’ve actually incorporated the UPS into the server itself. (See this article)
What they do is basically refit the power supply with a battery, intelligent charger and some DC/DC conversion. This makes perfect sense, as you gain efficiency by removing the DC-AC inverter stage as required by all other UPS systems, raising the efficiency from low 90′s to over 99%.
The trouble with this however, is that you can’t actually post fit. You need to have your server built with this technology incorporated at the beginning, and Google custom build their own servers in any case.
There is one big drawback however, and that is they’ve completely ignored power quality. It’s all very well making systems more efficient, but to do so at the expense of power quality seems false economy to me.
An Uninterruptible Power Supply does more than provide battery backup, it should condition the utility power so that any transients, surges, harmonics and all power quality problems are eradicated before they hit your server. Google’s approach seems to ignore this and they may be leaving themselves open to power problems as a result.
I agree with the decentralised approach however, you put the UPS in, as and when needed, saving the upfront costs. Ensuring the UPS are at capacity also has the efficiency benefit. Any problems with the UPS can be easily rectified (and will only effect the server it’s attached too) and probably more importantly, the UPS makes sure that only clean power enters the server.