Link: File crash consistency and filesystems are hard
Dan Luu's File crash consistency and filesystems are hard is about what it says it's about, with examples and interesting academic citations (that are kind of depressing) and the whole lot. If you want more reading, it has a whole bunch of links to further papers that you can go through. Most of them are apparently depressing reading, because the capsule summary is 'this stuff is hard and almost no one gets it completely right'; not user programs, not filesystems, and not the actual disk drives.
(Sometimes the 'not getting it right' bit is more accurately called 'cheating in the name of good benchmarks'.)
(I have a long standing interest in this area, as do many sysadmins. People tend to get upset if our systems lose their email during power failures and so on. Sometimes we cheat, but we like to do this with our eyes open.)
Link: Git from the inside out
Mary Rose Cook's Git from the inside out is a highly detailed and thus fascinating recounting of exactly how Git's graph structure and on disk tracking of things works as you evolve a repository. I knew many of the broad strokes just from general git knowledge but the details are illuminating and quite useful, especially the details around what exactly happens and gets recorded where during more advanced operations like merges (especially with conflicts) and pulls.
(I care about git things at this level of detail because they let me understand what's going on and what I can do about it when things don't go the way I expect them to. I'm not left poking futilely at a black box; instead I have the reassuring feeling that I can at least peek inside.)