The recent interview with Dave Cutler mentioned this briefly. When the Cairo team was working on their object file system, they had no requirement to maintain b

The recent interview with Dave Cutler mentioned this briefly. When the Cairo team was working on their object file system, they had no requirement to maintain backwards compatibility (which makes sense for new development). But they didn't build in a way to have in-place upgrades after it would have been released, either. The Tukwila team, still working with the old codebase, had a rule that NTFS could be upgraded, but it had to either accept the old file system structures, or be upgraded in-place. And their code allowed for that. Relevant portion starts at about 2:10 https://www.youtube.com/watch?v=xsQBKkPj5Nc https://www.youtube.com/watch?v=xsQBKkPj5Nc