See what I’m still not getting though, is how there can still be unmapped or retired areas, if the drive has been filled with (meaningless) data? Let’s say it isn’t all zeros, but random data instead. Are there more physical blocks than is represented logically by the adress space exposed to the OS?
On big flash memory you typically have more memory on the chips, than ia presented to the OS. Flash has significantly less write cycles, before the block breaks, so the controller monitors the health and won’t use it anymore when it will soon fail. Instead it uses a block from its unused extra space. (Details might be different, I’m not sure about that). This way the lifetime of the SSD is significantly improved. SD cards do the same, I think.
So the data in the retired blocks will remain and cannot be overwritten by the OS. If they are encrypted and the keys deleted, that won’t matter
See what I’m still not getting though, is how there can still be unmapped or retired areas, if the drive has been filled with (meaningless) data? Let’s say it isn’t all zeros, but random data instead. Are there more physical blocks than is represented logically by the adress space exposed to the OS?
On big flash memory you typically have more memory on the chips, than ia presented to the OS. Flash has significantly less write cycles, before the block breaks, so the controller monitors the health and won’t use it anymore when it will soon fail. Instead it uses a block from its unused extra space. (Details might be different, I’m not sure about that). This way the lifetime of the SSD is significantly improved. SD cards do the same, I think.
So the data in the retired blocks will remain and cannot be overwritten by the OS. If they are encrypted and the keys deleted, that won’t matter
Okay, that makes a lot more sense then. Thanks!