On the first occaisions, the MBR or the partition table drive was corrupted and the data was not accessible by Windows. I do not know if the data was accessible directly (through the SATA interface), but probably not. It didn’t matter, since it was a backup and I still had my primary data, so I recovered the drive and tried again.
It would have been available if using a tool such as TestDisc.
When it failed for the final time, I extracted the disk from the enclosure and found that the disk itself was in perfect condition, and the structure of the disk (MBR, partition table) were damaged. I am certain I could get the data out, if it mattered. Installed internally as an SATA drive, zeroed out (to make sure there was no problem), format, and no problems since.
