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This feature necessitates flash memory being overwritten with a random pattern twice as this helpsĮnsure that all memory blocks are overwritten. Security Control: 0359 In flash memory media, a technique known as wear levelling ensures that writes are distributed evenly across each To quote the ISM (Australia's military standards for cyber security). If a sector containing sensitive data exceeds such correctable error threshold, it will never be written to again, so the data in it will be there no matter how many times you overwrite the disk. Additionally, wear leveling is not based exclusively on write count, but also on the number of correctable errors in a sector. Wear leveling is nowhere near uniform write distribution, in fact, if a file stays on the flash drive for a long time while other content is written/removed/overwritten, sectors allocated to that file will have significantly less writes done to them, so they may be overwritten every single time during subsequent full-disk overwrites.
#Sandisk secure erase and clean full#
On such wafers, 5% to 10% of the cells are stillborn, and a few others will only last a few write cycles, while a decent flash card or thumb drive is typically specced to survive 100-500 complete overwrites.įurthermore, the chance of a random sector to survive N full overwrites (assuming 15% over-provisioning) is not 0.15^N. And this over-provisioning is much more significant that the difference between 1GB and 1GiB, in fact, the ability to use low-grade flash wafers is why the flash storage is so cheap.
#Sandisk secure erase and clean manual#
SanDisk microSD Product Manual tells it's an intrinsic function in their products. If you're still unsatisfied by this technique because there's a small probability that (a) a meaningful chunk of data survives and (b) the adversary will be able to read it out and (c) decrypt it, consider that physical destruction may not destroy the data definitely: there will be a chance that one night you will sleepwalk to a potential adversary and sleeptalk the data to them.Įdit addressing some of the comments: consumer-grade flash storage does have over-provisioning, e.g. Next time you're about to put sensitive data on a flash drive, consider encrypting it first! Strongly encrypted data is useless without the key, and if you securely erase the drive first, all that will be left is an occasional sector of such encrypted data surviving due to wear leveling.