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by eafer
1775 days ago
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The main problem is simply that people really really really don't like losing their data after they saved it to disk. A simple app that corrupts its in-memory state once a year is probably acceptable. A filesystem that corrupts its on-disk state once a year is pure garbage. You basically need to aim for zero bugs. How hard this is, it depends on the filesystem. Something like FAT, for example, is pretty much designed for ease of implementation, with few edge cases. Modern filesystems are not like that at all, the data structures are very complicated, so they must be extremely well tested before they are good enough to use. That would probably require an fsck to check for subtle inconsistencies; in the case of APFS you can use mine, but it's still very incomplete. Apple's published fsck is not very thorough. As an example of the kind of problems to expect, I recall a bug in the Linux HFS+ driver. If you had a drive with lots of short filenames and lots of long filenames, and you started deleting the short filenames, eventually you would lose half of your files. This kind of things happen because HFS+ has variable-length keys in the index nodes of its trees, so deleting a record may trigger a complicated cascade of node splits. APFS inherited this feature, and it was very annoying to implement. But HFS+ is very well documented; APFS is not, and that doesn't help. |
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