Comment Re:srm -v -z (Score 2) 91
Well, it confounds it at any rate. But completely filling the device's memory 33 times in a row is pretty likely to overwrite everything at least once or twice - even the hidden "failure reserve" space if it's included in the wear leveling (and if it's not, then it doesn't yet hold any sensitive data, so there's no problem). Guttmann's values may be irrelevant to today's storage media, but that many repeated rewrites of anything still mostly does the job.
If you were an engineer in charge of destroying data printed on paper, and you decided on shred then burn then stir the ashes in water, how many times would you repeat the cycle in order to be sure the data was destroyed? Hint: if your recommendation is greater than one (in order to be pretty sure), check your job title, because you're probably Dilbert's pointy-haired boss.
Drives today work almost nothing like the drives of 20 years ago. They don't paint bit-bit-bit in a stripe, they encode a set of bits in every pulse of the write head. Alter it a tiny fraction, and it becomes a completely different set of bits, one that error correction won't be able to overcome.
Old disks were recoverable because the mechanisms weren't precise, and the data was written with big chunky magnets to assure it was readable. All that slop has been engineered out on order to achieve today's remarkable areal densities. One overwrite is all it takes - as long as you're overwriting it all.