Alan McKinnon writes: > On Thursday 17 December 2009 02:37:54 Robert Bridge wrote: > > dd is pretty thorough... afterall, it writes to every single block on > > the disk. > > And the resulting effect from doing that once is: > > Trivially easy to recover the data that was there just before you did > the dd > > Why? Data on-disk is not a binary cell like ram. It is a magnetic > pattern and the pattern from the previous write is still there IIF you > know how to find it
I disagree here. In theory it may be possible, but trivially? Seems no one ever did it yet. From <http://www.h-online.com/newsticker/news/item/Secure-deletion-a- single-overwrite-will-do-it-739699.html> : They concluded that, after a single overwrite of the data on a drive, whether it be an old 1-gigabyte disk or a current model (at the time of the study), the likelihood of still being able to reconstruct anything is practically zero. Well, OK, not quite: a single bit whose precise location is known can in fact be correctly reconstructed with 56 per cent probability (in one of the quoted examples). To recover a byte, however, correct head positioning would have to be precisely repeated eight times, and the probability of that is only 0.97 per cent. Recovering anything beyond a single byte is even less likely. Wonko
