[malfist]

It does degrade, but not performance. The degrading happens when blocks hit their wear limit and can no longer be used. Flash memory typically includes additional blocks to replace those that are at their wear limit, but that will eventually exhaust and then the drive will be in a failure state. This can sometimes be that the drive stops working, or that it shrinks it's capacity, but the bandwidth and access speed characteristics remain constant throughout it's life.

[ssl-3]

How does a storage device shrink in capacity, and by what mechanism is that shrinkage communicated with the filesystem?

[malfist]

That's determined by the firmware and the manufacturer.

Flash isn't like disks. You don't write to a block that's on a certain cylinder on a certain platter. You write a block and the memory controller determines where it will be stored, usually based on some wear leveling algorithm.

It's one of the reasons you can't securely delete a flash drive.

[ssl-3]

The question remains.

Handwaving about how flash is different than disks isn't an answer to how shrinkage is conveyed to the filesystem (and isn't a meaningful differentiator anyway, since common spinny-disks haven't been 1:1 mappings for well over 3 decades, themselves).