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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?

Ray Woodcock
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There are a couple of different things at play, and some wrong information.

The SSD does, indeed move data arround. This happens at a level underneath the OS, and the SSD presents, more or less, as a regular hard drive - is the SSD firmware tracks these changes regardless of OS.

On the other hand, multiple overwrites with something like DBAN ARE likely to overwrite data so it can't be recovered (except for cells marked bad) which are not actually bad. Crucially, however, because of over provisioning you need to overwrite with more then 1 pass, and no one will guarantee you everything will be overwritten .

You should use Full Disk Encryption in future to avoid this conundrum (also seeif your drive supports secure erase which will also wipe everything securely)

davidgo
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