Long story resumed: I improved the situation, yet I am stuck now
- A girlfriend's faulty 1Tb External usb HDD with NTFS partition took about 10 minutes to mount on my Mac X.12.6 and then appeared empty in the Finder
- The Mac Disk Utility could detect after a long time 540Gb and 607 files in the faulty HDD
- The third party commercial Stellar Phoenix Mac Data Recovery software could easily show the full tree structure and files of the faulty HDD. But no recovery without a licence
- I successfully used DDRescue_GUI to dump the content of the faulty 1Tb HDD onto a healthy 1Tb
- The healthy HDD mounts immediately, but still appears empty in the Finder and with 540Gb and 607 files in the Disk Utility
- Stellar shows the exact same full tree structure and files on the healthy HDD. But, I still wan't to find a really free solution to recover all the data (or as much as possible)
- Sudo TestDisk only lists "." and ".."; It proposes a corrected rebuild sector but can't write it. it "can't write new MBR code", "can't write new NTFS boot sector" (and NTFS boot backup sector). And it indicates: "MFT and MFT mirror are bad. Failed to repair them"
PS: I am only slightly computer literate, and amazingly there is a lot of probably basic computer vocabulary and concepts that I don't understand.
Here is a couple of them:
- the MSDos checkdisk /F : if used, does it erase the existing MFT ?
- The tree structure and file names: is it not stored in the MFT ?
- A read only HDD: how to make the HDD writable again ?