Clearing the unallocated disk space

[jd1008]

On 11/16/2014 09:46 PM, Bruno Wolff III wrote:
>>>> On Sun, Nov 16, 2014 at 2:04 PM, jd1008 <jd1008 at gmail.com
>>>> <mailto:jd1008 at gmail.com>> wrote:
>>>>
>>>> Before sending the drive for warranty service, what is the best
>>>> way to clean the unallocated blocks?
>
> If this is really important to you, just eat the cost of the drive and 
> destroy it instead of sending it back.
>
> If not modern drives provide a secure erase function and you should 
> use that. You can use hdparm to do this.
Thank you Bruno.
I had come across some sites a couple of years ago that claimed all 
modern drives
have some number of gigabytes that are not touched by hdparm and are
also untouched by using dd /dev/zero into the unmounted disk.
How can anyone ascertain this unless one is a disk drive HW engineer
and can tell the pieces of electronics inside the disk, and even on it's 
controller.
If any part of this is true, then destruction seems to be the only 
alternative for
all security and privacy minded users.