Overlayfs doesn't write through, and I believe unionfs and aufs no longer support write-through. What I want is pretty much like how a write-through cache woul

Overlayfs doesn't write through, and I believe unionfs and aufs no longer support write-through. What I want is pretty much like how a write-through cache would work. 1. Write to top-level FS? The write cascades down but reads are fast immediately 2. Data not available in top-level FS? The read goes down to the bottom level and then reads up to the top so future reads are fast.