[lmm]

The difference between a file system and a container format is mostly a matter of perspective - indeed OSX literally uses "disk images" as their container format. Is .zip a filesystem? You probably wouldn't want to use it natively on a disk, but for a lot of purposes it's the same kind of thing.

[ValentineC]

Many SSDs (I first learnt about the concept from those notorious SandForce SSDs [1]) also utilise compression at controller level to reduce wear.

So yeah, many SSDs are just huge, non-solid archives.

[1] https://en.wikipedia.org/wiki/SandForce#Technology