The home storage boxes now on sale are advertised with redundancy as the headline, and a great many people are reading that as protection. It is not, and the gap between what it does and what buyers think it does is the most dangerous thing about the product.
Redundancy defends against exactly one event: a disk failing on its own while everything else continues working. That is a real event and worth defending against. It is also a small fraction of how data actually disappears.
Delete a folder by mistake and it vanishes from every disk simultaneously, because the array is doing precisely what it was built to do. Let a corrupted file be written and the corruption is faithfully mirrored. The controller can fail and scramble an array that was mechanically perfect. And the whole box sits in one room, so fire, theft, and water take it exactly as they take the computer beside it.
Then there is the rebuild, which is the part people find out about at the worst moment. Replacing a failed disk means reading every block of every remaining disk to reconstruct what was lost, which on a terabyte drive takes many hours at sustained full load. The surviving disks are the same age, from the same batch, with the same hours on them, and you have just given them the heaviest work they have ever done. A second failure during rebuild is not an unlucky coincidence. It is the single most likely moment for one.
What worries me most is the behavioural effect. I wrote in May that the hard part of backup is location rather than storage, and this makes the location problem worse by resolving the anxiety that would otherwise drive somebody to fix it. A person who buys one of these feels protected, and a person who feels protected stops copying things elsewhere.
So the product can leave you in a worse position than the single disk it replaced, not through any defect, but because it removed the worry without removing the risk.
These boxes are genuinely good at what they are for, which is keeping a large collection available to several machines and surviving a mechanical failure without an afternoon of downtime. That is worth the money. It is a convenience feature that happens to have a reliability side effect, and it is being sold the other way round.