7 Jan
2016
7 Jan
'16
2:12 a.m.
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