[CentOS] help fdisk and dd

[Mike McCarty]

John Doe wrote:
> From: chloe K <chloekcy2000 at yahoo.ca>
>> What is the best practice to remove all data in the disk?
>> ls fdisk ok or use dd 
> 
> Maybe something like (replace the ?):
>  - fast but not secure:
>    dd if=/dev/zero of=/dev/?d? bs=4096
>  - slow but more secure:
>    dd if=/dev/zero of=/dev/?d? bs=4096

What is the difference between the above two commands?
Did I miss something?

>  - n times slower but n times more secure:
>    for ((i=1; i<=n; i++)); do dd if=/dev/zero of=/dev/?d? bs=4096; done

I don't know what "n times more secure" means. Could you
please explain? Does that mean that, with n times as much
work, one can still recover the information?

Mike
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