[heise online UK] Secure deletion: a single overwrite will do it

[Jason]

On Mon, 19 Jan 2009, Stefan Kelm wrote:
> ... and who knows where else? Really, to ensure that nothing more can be
> recovered from a hard disk, it has to be overwritten completely, sector
> by sector. Although this takes time, it costs nothing: the dd command in
> any Linux distribution will do the job perfectly.

I agree in general, although you still have to watch out for "reserve tracks" 
(search on this page):

http://forum.hddguru.com/seagate-terminal-commands-t6411.html

"All hard disks have reserved sectors, which are used automatically by the 
drive logic if there is a defect in the media.":

http://cisn.metu.edu.tr/97-2/hardware.html

Those could perhaps be used to smuggle data out of a wiped disk.  Or, if your 
disk firmware is (or someday becomes) clever enough to transparently swap out 
dying sectors with those from its reserved store, you could accidentally end 
up with data on the disk that dd would miss.

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