Why does a central London colocation data centre need backup generators to its backup generators?
The data centre and colocation industries are mission-critical. The consequences of a failure of electrical power to the electronic equipment a colocation data centre supports are severe. Generator systems are often specified and installed at N+1 or 2N, meaning there is at least one backup generator available in case a backup generator fails to work. So why doesn’t everyone else in mission-critical environments do that? Office buildings are nowadays often specified with backup generators, but rarely at more than N+0. London data centres are mission-critical, but if there is a failure it isn’t a matter of life-or-death. In a hospital such a failure really is a matter of life-or-death. People die on operating tables if the power stops and die in beds if dialysis machines stop. Hospitals don’t usually have N+1 generators, so why do London colocation data centres need them? Even Dealing Rooms don’t have such levels of support (although the trading platforms which are in London data centres do).
Is it just about marketing – the competitors say they have N+1 so we must have it too? Or to meet the requirement for Tier Levels? Is it really needed for mission-criticality? Or is it just fashion? Or perhaps it’s to guard against poor Facilities Managers who may not do the maintenance properly.
Consider Tier Levels. These are defined by a commercial organisation in the USA called the Uptime Institute which has copyright protection on the designation. They are highly US-centric and reflect US conditions. Texas, for example, has frequent hurricanes and tornados. Much power distribution is on overhead lines because of the distances involved. So long power outages are not uncommon. Florida has frequent lighting strikes (Tampa is often described as “the lightning capital of the world”, fairly or not) which can result in serious prolonged outages. Do specifications designed for such places have any place in a sophisticated and temperate environment like London? A London data centre is sometimes described as a place where power outages are rare occurrences and only fleeting when they happen.
That is not the experience of City Lifeline, a London colocation data centre, right in the heart of London. We experience a short outage, just long enough to start the generators, maybe once a year. But in May 2008, we had a 6-hour outage on one feed and an 8-hour outage on the other (when the Whiston Road substation in East London blew up). That was followed by an 8-hour outage on both feeds exactly two weeks later. In May 2010, we had a 16-hour outage on both feeds for reasons which were never explained. So the Utility providers should provide SLA’s, guarantees and compensation, right? They don’t. They provide power if and when they can. If they don’t, well that’s a pity but never mind.
Above all else, a London data centre must be reliable and offer reliable London colocation to its customers. Mains electricity, no matter where, is not reliable. So who would design a reliable London data centre system that depended on an unreliable supplier?
The answer to this is that a London data centre, whether a London colocation data centre or not, does not run on mains electricity. It runs on diesel generators and must be designed so that the backup generators always work. In other words, the backup generators are the primary source of power for a London data centre. Mains electricity is there because it is cheaper than running diesel engines (by a factor of about 2:1, assuming that it would ever be possible to get planning permission to run high-power diesel engines continuously in somewhere like central London). Mains electricity is the secondary source of power, sometimes referred to as the “economic alternative” which leads to the odd and counter-intuitive situation where the primary source of power only operates 0.1% of the time and the secondary source of power operates 99.9% of the time. But it has to be that way, because only the diesel generator source of power can be made to be reliable to the standard required for colocation in a London data centre.
That thinking also leads to an interesting result from the question “How many mains feeds are best for a London data centre?” Everyone will be familiar with the salesman who pushes the idea that his data centre has two or three or four mains feeds and is therefore the best because of it. But if the mains feeds are only the “economic alternative” and exist solely to reduce the data centre operator’s power costs, then why does it matter how many feeds there are? The data centre has to be designed to work continuously at 100% performance level with any or all or none of them working. So perhaps having one mains feed is just as good as having four, even if that is not what Marketing wants to hear.
A London colocation data centre does need backup generators to its backup generators. If the generators are the primary source of power – the one that can never be allowed to fail – then N+1 or 2N is necessary to guarantee the integrity of the power supply. Mains cannot be relied on. And Marketing requires it too – if the London colocation competitor down the road has N+1 generators, then the London colocation competitor which cannot match that will fall behind in its customer’s perception.
Roger Keenan is Managing Director of City Lifeline, an independent central London colocation data centre. This article is based on a presentation given at Data Centre World 2012.
