I naturally understand why this is. We always say “more moving parts makes there more chance for failure”. But why is this? Is it just how the universe has to be due to the laws of physics?
For instance an airplane is pretty complex but the aluminum that makes up the structure of the plane rarely needs to have complete overhauls while something like the engine is constantly being serviced and kept up to standard.
What is it about spinning parts, heat, and lots of piping that make something constantly be trending towards breakdown?
In: Engineering
Failures while running are generally spread out randomly over time, the more possible points of failure you have the greater the chance that one of them will come into play.
Consider a server with a bunch of hard drives in it and each individual drive has a Mean Time Between Failures of 1,000,000 hours. If you have a single 10 TB hard drive then you only have a 50% chance that it’ll fail in the next million hours(that’s what MTBF tells you). Now what if you have two 5 TB drives? The chance of each failing in the next million hours is 50%, but the chance that one of the two will fail is actually 75% and you have a 50% chance of failure by 500k hours. Now what about 16 drives? Now you’re down to 62.5k hours simply by adding more components to the system even though they’re all just as reliable. This is why big servers will generally have some redundancy so they can tolerate one or two drive failures without losing data because they *will* have failures every year.
If any single failure point can take down a system then the more of those failure points you have the more likely the system is to go down even if each failure mode is very unlikely.
Luckily a lot of failure modes in big systems like cars and planes are wear out so we can proactively swap parts like the bearings and tires to avoid a catastrophic system failure that can happen if the failure is random and occurs at an inconvenient time.
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