Power cut in central London today – Quick, get down the shop and get more AA batteries!

Power Cut!

We were in with some customers today around Liverpool Street in central London when there was a power cut (link). Initially we just thought the building was out of action but shortly afterwards we realised all the traffics lights and services in the area were in trouble too. We were all rendered useless without email and web access as the visitors wifi access point was one of the first victims of this power cut (Worrying how dependant we have become!). Desperate times, desperate measures, so we decided to relocate to the nearest watering hole (which was packed for that time of day!)

The events of the day got us talking about UPS protection and how long a server, data-centre and even are area could survive on UPS protection. One of the customers who joined us runs a company data-centre and he commented that theres about 40 minutes worth of UPS protection which protects their critical infrastructure….

The power cut began around 3pm and power was restored around 8pm. Our poor customers data-centre began it clean shutdown 4hrs20mins before power was restored! Around 3:45pm, I suggested they should have been running our ARM Viridis servers in their data-centre. The local sys admin grunted and sighed. Restoring the company infrastructure from scratch was a job that was going to take some time.

What if they had been using our ARM Viridis Server?…

I didn’t have numbers for the UPS but lets assume something along the lines of a 3000VA UPS (link). This would last for 40 minutes at about 1500w. Lets also assume the servers were running at 100% load (for ease of calculation rather than typical use case), we would have 8.5w for a Viridis server (link) or 390w for a E5-2680 server (link, ref Table1)

Servers Type # of Servers/Cores Power Consumption Lifetime on UPS
Intel E5-2680 4 servers / 64 cores 1560w 38.4mins
Viridis Cortex A9 180 servers / 720 cores 1530w 39.2mins
Viridis Cortex A9 16 servers / 64 cores 136w 441mins / 7.3hrs

So an equivalent number of ARM cores would have survived on the company UPS! Shame it took a real power cut to realise this..