[Cryptography] Ex-CIA Joshua Schulte Describes His Data/Crypto Hiding Prowess

[Jerry Leichter]

>> The first thing I do with every new storage disk/SDcard is: dd
>> if=/dev/urandom of=/dev/sdX; ...
>> 
>> So now *all* of my slack space contains random data.
> [...]
> 
> Solid state storage devices typically have some (one reference I
> found suggests 7.3%) of their physical blocks hidden in reserve to
> accommodate reshuffling around bad blocks and to ease transparent
> wear levelling. The "physical" block addresses to which your
> operating system's device driver writes aren't all the actual blocks
> on the device, nor even the same actual memory locations each time
> you "fill up" the ones it tells you are there.
All of this has been true on spinning rust drives for many years.  One common approach was to leave one sector free on each track.  If a sector goes bad, remapping is trivial - basically you just "slide the track around" so that the first sector is the one just after the bad block.  This requires minimal memory - the physical "first block" - and CPU power, important back in the day.

These days, the processing power and memory embedded in a disk drive renders the cost of doing more sophisticated remapping irrelevant.  It's generally pretty much impossible to know what's going on inside of a modern disk drive.  (Google put a lot of effort into understanding the performance implications, but even Google couldn't get much info out of the drive makers.  They had to do some sophisticated testing to figure stuff out.)
                                                        -- Jerry