I used to do stuff like writing a 0 to every part of the drive making recovery harder. dd if=/dev/zero of=/dev/replace_with_devID
or writing random data to every part of the drive or using a tool like dban
(Darik's Boot and Nuke) to wipe drives that were going to be given away as it was marketed as using some DoD specification for data destruction.
But those methods are extremely time consuming. So I decided to watch videos about how data recovery was done to get ideas of how to make it not worth the effort and as I can't remember what data was once on X drive... I assume every drive contains sensitive information an destroy it.
Remove the spindle and separate the individual platters.
When trying to recover data from faulty drives a common technique is moving the spindle to a donor drive of the same model. This apparently requires the platters to not move from their locked position otherwise full data recovery becomes much harder as data is usually not contiguous and a table exists that is pointing to where every part of a file is across the entire drive.
Scratch the platters.
It seemed data was often difficult or impossible to recover when there was physical damage such as where the read head had crashed into the disk. So I take the individual platters, place them on concrete and move them back and forth repeatedly scratching the absolute hell out of it way worse than a drive head could. Eventually this became tiresome and started using a angle grinder to speed up the process and ultimately cut each platter in half just to make it more difficult to work with. This can be dangerous so... yeah, be safe.
Smash the chips on the drives circuit board.
I broke the SATA connector on a 3TB drive and wanted to repair it. I thought I could just swap the circuit board but from reading, for my particular drive it had a special chip. I needed to get a new board for my drive and transplant a specific chip from the original circuit board to the new one. So I now make sure to destroy all the circuit boards even though not all drives are like this.
Governments often require drives that held sensitive data to be shredded into tiny pieces so I assume that partial data recovery may still be possible from my above suggestions but the number of people capable of doing so is very small, it would be very time consuming and none of us are worth that effort.