DSL Ideas and Suggestions :: Unionfs

just a FYI...when you run mkwriteable the contents of the system are not copied into ramdisk....it's mostly just symlinks. For the most part the actual files are still located in /KNOPPIX. The difference is that the individual files are now linked, rather than just the base directories, so adding to the dirs is possible.
Although there is an increase in RAM usage, it's not as bad as you may think.

original here.