On Tue, 5 Jan 2016, Fred Cisin wrote:
1) if the alignment of the head of the original recording and of the overwrite head are not a perfect match, then there can be some residual data somewhat off axis.
At a first thought I don't see how there can be residual data because there is the tunnel erase head after the R/W head. The drives must be very misaligned (i.e. more than the width of one erase half) to still have residual data.
2) if the data was overwritten once, with a known pattern, then somebody with sufficient resources and motivation can attempt to analyze the noise, and determine "what, overwritten by a 0 could produce the noise that we have here." Accordingly, there are guvmint standards of MULTIPLE patterns to
That is why you don't take /dev/zero but /dev/[u]random for overwriting data.
Christian
