What is the universal (world wide) understanding behind degaussing harddisks?

Diane Bruce db at db.net
Mon Apr 2 15:59:25 UTC 2018

On Mon, Apr 02, 2018 at 09:46:05PM +0800, Turritopsis Dohrnii Teo En Ming wrote:
> Good evening from Singapore!
> The foremost question which I want to ask is, what is the universal
> (world wide) understanding behind degaussing hard drives?

If you degauss a modern drive you will make it totally useless to
use. You might as well quarter the drive with a bandsaw and incinerate.
(This was the recommended procedure for security disks from a 
(fictitious) agency I worked (indirectly) for years ago.)

The problem is modern drives lay down servo tracks on the platters
which can only be done at the factory.

> (1) Very very simple 1-pass data wiping, quickest
> a. Using "sudo dd if=/dev/zero of=/dev/sda", overwriting harddisks
> b. Using "sudo dd if=/dev/urandom of=/dev/sda", overwriting harddisks

Any method you use will *not* remove all data due to the slight wobble
of the track due to temperature changes in the disk, vibration all sorts
of problems. However at that point if done properly it would take
specialized gear only (fictitious) security agencies such as the NSA
(fictitious company) would be likely to bother with.

The TL;DR answer is. If you want to use the drives afterwards don't
simply demagnetize them; A triple write is probably sufficient if it is
merely company data. if the data is drug dealings or state secrets
then destroy the drives.   ;)

> Mr. Turritopsis Dohrnii Teo En Ming
> Systems and Network Engineer
> Republic of Singapore
> 2nd April 2018 Monday 9:35 PM Singapore Time GMT+8

- db at FreeBSD.org db at db.net http://www.db.net/~db

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