So I've been using overlayfs for a while during my unsane pseudo-embedded Gentoo experiments, this filesystem is currently under active development but has yet to be merged into the mainline Linux kernel (the last attempt for 3.10 didn't made it).

For this reason I managed to merge an old version over the sunxi kernel and despite the fact this filesystem it's still experimental I found this specific version (overlayfs v11 over kernel 3.0.101) mostly stable for a daily driver.

If you own a development board based on Allwinner Socs (A10, A10s, A12, A13), like my Olinuxino A13 and you need an overlay filesystem just give it a shot: 

• https://github.com/x-drum/linux-sunxi/tree/sunxi-3.0-overlayfsv11 (tree)
• https://github.com/x-drum/linux-sunxi/releases/tag/3.0.101-ovl11 (download)