Close please.
The 17G was from trying to blank the drive, which for some reason
disconnected in the process resulting in a file written in /dev with the
name sda. From there on the loop and so on. So there was a /dev/sda file
as a left-over after that. Thanks for pointing me in the right direction
and apologies.
I am going to continue investigating why I got the data corruption in
the first place, before I tried to blank it, but it looks like it may
have been a hardware issue with the original USB-to-ATA bridge.
--
Anton R. Ivanov
https://www.kot-begemot.co.uk/