Human Error: The biggest challenge to data center availability and how we can mitigate – Part 1


The 2016 Ponemon Institute research report on Cost of downtime (reference 1) contains a chart showing the cause of data center downtime, and classify accidental human error to be 22%, and the top six contributors to downtime are UPS system failure (25%), cyber crime (22%), accidental human error (22%), water/heat/CRAC failure (11%), weather related (10%), and generator failure (6%). However, the accidental human error did not account for latent human error that could have contributed to those UPS/CRAC/Generator failure.


Uptime Institute had cited 70% of data center outages can be attributed to human error.

The definition of human error is broader and can be generally classify into Active Error (where a deliberate action caused deviation from expected outcome), and Latent Error (where a non-deliberate action caused deviation from expected outcome). For example, when a design decision is made regarding the power protection circuit for a data center room, if it was not fully co-ordinated to isolate and protect power issue to cascade upstream to higher level circuit breakers.

There are many cases of major outages in the past few years that are attributed to human error. The 2016 Delta airline data center outage is reported to cost them USD 150 Millions. Part of the long delay (3 days) to resume service is that a significant part of their IT infrastructure is not connected to backup power source which begs the question why did it happen that way? Well, it should be due to latent error, where the IT equipment installation or the in-rack PDUs are not from two separate UPS or supported by in-rack ATS switch.

I was asked a question during my presentation on this subject matter whether higher tier level aka higher resiliency designed and implemented data center can minimize this issue of human error. My answer is you can design and implement to 2N power and cooling infrastructure, but when 1N is taken down for maintenance, any mistake or weakness (inexperience operations staff/vendor personnel, procedure gap that human nature overlooked and made wrong guess etc) can take down the IT load and has happened to many data centers (google search on human error and data center outage incidents).


There are multiple ways for the human error to manifest in a data center outage. They can be simple external trigger that goes through loopholes like the Swiss cheese above, or cascade (combination), or direct active human error.

For example on cascade, a case of lightning strike that caused momentary power dip (see reference) should not cause an outage in a data center; however if the selection of circuit protection device or the design did not cater for how the DRUPS would respond in such a situation, and the automated control was not configured to deal with it, then any amount of SOP/MOP/EOP or Method of Statement-Risk Assessment (MOS-RA) may not protect the facility against a particular external trigger. A case of a data center in Sydney whereby the circuit breakers were not designed and selected to cater to such a scenario caused the UPS to supply to the grid instead of to the load.

For direct human error, I have also known a case of UPS manufacturer trained and authorized service engineer causing an outage, where the engineer did not follow the documented service manual and caused the entire set of UPS to tripped, and because the circuit protection devices were not able to isolate the fault downstream, caused the upstream incoming breaker to trip. This is part of the reason why data center staff should accompany and question the service engineer at critical check-points during servicing of critical infrastructure.

Outage can be failure of the resilient design / implementation due to under-capacity. This can be traced to latent (no tracking of actual power capacity versus designed capacity) or active (no checking of UPS capacity before maintenance). For example, actual power usage of N+1 UPS has actually become N UPS, and when one of the UPS was down, the entire UPS set shutdown.

In the next post, measures to mitigate the risk of human error will be discussed.


Human Error: The biggest challenge to data center availability and how we can mitigate – Part 1

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