The difference here, though, is that NTFS does not have BTRFS's reserved area at the start of the volume. The BTRFS converter has to relocate foreign data stru

The difference here, though, is that NTFS does not have BTRFS's reserved area at the start of the volume. The BTRFS converter has to relocate foreign data structures out of that reserved area, meaning that the volume is not simultaneously both the old and new formats. Ironically, given what I mentioned, this conflicts most heavily with FAT. Whereas the only fixed-position data structure in NTFS is the BPB in the Volume Boot Record, which it can even mostly share with FAT. In the FAT to NTFS conversion there is a point where (BPB aside) the two sets of filesystem structures are simultaneously valid.