Hindsight in filesystem design
NT4 (NTFS 1.2) did not store numbers of MFT records. If MFT became fragmented, it appeared that there are millions of file records linked in the tree based on the record numbers. However, it was difficult to establish what number belonged to what record. Algorithms for detecting record numbers were complex, unstable, and requiring a lot of resources. Starting with Windows XP, the MFT entry number is stored inside the entry itself that, as it was planned, had to facilitate data recovery. When the volume was updated, for example, when a volume created in NT4 was connected to Windows XP for a first time, all records remained in the old format, without numbers. Records were brought into a new format only when a file, which the records referred to, was changed. So, we were encountering hybrid volumes over the several years thereafter. When at last, users ceased to format disks using NT4, all the records were numbered and data recovery software eventually stopped to support the ...