Comment by andrewaylett

It's not power failure I'm worried about, it's failure of other systems. But even so, yes, it's more likely that the systems that are supposed to ensure redundancy will fail than the otherwise-non-redundant services.

For what it's worth, my house isn't a single power domain -- I'm running some of my services on an old laptop that's still got some battery. But it goes to sleep if the power goes off, and needs physical intervention to recover. Which is an excellent example of redundant systems providing multiple single points of failure and of the perils of using random left-over hardware to run stuff.