@nazokiyoubinbou @nixCraft Overwriting 10x is only sensible for (very) old hard disks or floppy disks with wide tracks. Current hard drives pack tracks so close that writing one may impact neighbouring tracks.

So overwritung the complete disk once (e.g. 'dd bs=1M </dev/zero >/dev/sdX' on linux) will do the trick. On SSDs, due to wear leveling algorithms parts of data may survive overwriting in spare sectors but reading date from there will be hard.