Wow. Lots of thoughts. First off, if we're talking about the same thing(s) I'm in violent agreement. However I question that congruence. First observation is t

Wow. Lots of thoughts. First off, if we're talking about the same thing(s) I'm in violent agreement. However I question that congruence. First observation is that one light isn't a reliable on/off indicator because the light can fail; you need two lights, one for "on" one for "off". Then at least if no lights are showing you know one of them is broken. OTOH a meter which reliably reads 50% of actual or consistently jumps between 30% and 70% violates the principle of least surprise, but I can work with it once I know about it as long as there aren't too many competing distractions. Sometimes a broken indicator is better than nothing; sometimes it's worse. People ask me to do a lot of tasks applying deterministic logic to nondeterministic systems (at lot of this comes down to lack of research, although the reasons for this lack of research vary; I don't accept these kind of jobs without asking some pointed questions first). Sanity checks feel kind of pointless here, because what would they mean? I've surrendered to the philosophy that feeling that I know what is going on is sanity; therefore the sanity check is I feel like I know what's going on. The approach I've settled on is "bug parts", or measuring the actual ingredients and including that in a label. In practice this means that I report certain (often reverse engineered) values, and count the number of times through various portions of code and report those. In reality it seems like the good ones collect in some distinct buckets or fingerprints (and I keep adding indicators until this occurs!); anything which is not in one of those buckets could probably use a closer look. There are different ways of reporting disk (and memory) space. A common example of this is "copy on write"; a common corrolary is "start with zero". If this is being done, large chunks of a randomly written file might not be allocated and if you read them you get zero. This presents a problem for "space which is used": does this represent the commitment (this is a 30GB file), or usage (4GB is allocated, the rest is all zero)? Finally, in a twist on that last point systems overcommit. Your allotment might be a limit, not a contract.