From kernel Documentation/bcache.txt: > You'll need make-bcache from the bcache-tools repository. Both the cache device and backing device must be formatted be

From kernel Documentation/bcache.txt: > You'll need make-bcache from the bcache-tools repository. Both the cache device and backing device must be formatted before use. So, it's far from overlayfs. I could accept formatting the cache device, but not the backing storage.