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> That is exactly what TRIM is, a mechanism for a filesystem to tell the
> drive "this block is no longer in use". Otherwise, the only thing the
> drive has to determine whether a block is in use is whether it has ever
> been written.

But, from what I understand, it doesn't exactly tell the firmware "this 
is no longer in use" so much as it says "you can zero this right now if 
you want"


>> Simply assuming based on if or how long ago it was written to can't
>> possibly be a workable solution. I'm not convinced that leaving large
>> chunks of the drive 'free' has any effect on wear leveling.
>
> It provides a pool of blocks that have not and will not be written.

Bbut how does the drive "know" that those blocks are not allocated by a 
partition somewhere and are safe to use as spares? It's not like the 
drive firmware reads into the partition table or anything.