No, I don't at all mean in general.
(See my cousin reply here).
That is not at all "about it". I mean, specifically, for the layer that a RAID produces. It's simple. When you add RAID, you add a layer on top of physical hard-drives to make them redundant.
This type of layer has a completely different expectation from all of your other examples. The example in my cousin reply is apt: it would be like expecting a checksummong algorithm (which you're ONLY using to add verification that a file is genuine) to sometimes fail and produce a random checksum in the space of possible checksums the algorithm can produce, instead of the checksum that the algorithm actually produces for that particular file. Or if it has a comparison function, to sometimes fail and say that the file checksums to the provided checksum, regardless of whether it does so.
This is ridiculous: such a layer wouldn't be a checksum, it would be completely different. The idea that I have to physically roll a layer on top of my checksum, to check whether it's currently acting like a randomized print statement or a comparison function whose truth value is randomly negated, is ridiculous.
I don't know how else to put this. Maybe instead of your RAM, bicycle, examples, I can give you these examples:
-> Imagine if you are adding a fuse to a circuit to protect it, but the fuse sometimes actually just saves up electricity so it can release it one quick burst and override the circuit. That's not a fuse.
-> Imagine if you hire an auditor to make sure your employees aren't misappropriating funds, since the business involves a lot of cash, but your auditor sometimes just pockets cash. That's not an auditor. You only thought you hired an auditor. The solution isn't to make sure the auditor has an auditor, it's to hire an actual auditor instead of someone you mistakenly think is one.
-> Imagine if you buy insurance, but actually the company sometimes will just spend lawyers on defending having to pay out, even when the event clearly happened and you were clearly covered. That's not insurance - that's a scam. You shouldn't have to insure the layer of insurance with an insurance against the insurance company out-lawyering you. You should get an actual insurance policy.
-> Imagine if you buy a seatbelt, but after buckling it, there is a realistic chance that you really haven't, and it's just a clothing item draped across your body and not attached in any way at any point.
Well if that's possible, that's just not a seatbelt. It's a defective item that was supposed to be a seatbelt but isn't.
The point is, all these examples are optional layers on TOP of a process. If they have a realistic chance of failing as in the above descriptions, they simply are not what they're claiming to be. Their chance of failure should be so low you can't even think about it; if it isn't, you should just hire or buy a different on, since you made a mistake.