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I am informed that drive wiping tools do not work reliably on SSDs due to such features as wear leveling. Here, for example, a quote from MakeUseOf:
[T]o comply with wear levelling, the SSD must constantly move data around the drive to ensure all blocks are worn at an equal rate. Using a secure “file shredder” to overwrite a specific file or folder many numbers of times is not going to work, because the drive writes all new incoming data to various different blocks, depending on its needs. Only the drive knows where this data is written . . . .
But explanations of TRIM seem to indicate that, in fact, only the OS knows where the data is written. For instance, Wikipedia says,
The TRIM command enables an operating system to notify the SSD of pages which no longer contain valid data.
These accounts seem to conflict. If the OS knows where valid data is located, then presumably the OS also knows where invalid data is located. In that case, the OS should be able to inform a drive wiping program of the blocks needing to be erased. Then, contra MakeUseOf, a file shredder should work.
What am I missing?
"What am I missing?" -- You're conflating the two layers that the SSD firmware deals with: the layer with logical sectors that the host OS uses and the lower layer of flash blocks and pages. You the user or the OS never knows exactly what is going on at that lower layer, i.e. where a "sector" is actually mapped in flash. – sawdust – 2018-03-28T05:56:04.097
There is a layer between the SSD flash blocks and the OS that the SSD uses to translate "logical" OS block addresses into flash block addresses. The OS has no visibility of this layer and so has no idea where a physical block is on the SSD. https://superuser.com/a/901521/19943
– Mokubai – 2018-03-28T06:07:29.590Two questions: (1) Why did this question get downvotes? and (2) Why do people sometimes answer questions by providing comments (i.e., here) instead of posting them as answers? (My reply to Mokubai's comment appears below.) – Ray Woodcock – 2018-03-28T18:03:21.283