I've been using unionfs-fuse but it's so slow (a compile will show 45% of CPU used by unionfs-fuse) so I'm switching to aufs on Ubuntu 11.04 with kernel 2.6.38-11-generic-pae (I guess that means I'm using aufs2) With unionfs-fuse I had my read only tree in two parts, one was a complete chrootable root build environment filesystem, and one was project build sources. Both have different origins and aren't easily combined. The project sources need splicing into a subdirectory of the build environment I would create an empty directory to hold RO mounts and into this I would bind-mount the build environment and in a sub-directory of that I would bind-mount the project build directory. All of this would then be mounted in a new directory with a cow by unionfs, and on top of that I would bind-mount some more project directories which do not warrant cow protection (because I'm working on them). Into this I would then chroot to build my project Aufs seems to give some problems. When I replace the unionfs mount with aufs, it mounts the RO mount point and carries through the build environment but it does not carry through the project build sources which were bind-mounted into a subdirectory. Note that the build environment that was carried through was not mounted directly by aufs, it was bind-mounted to a point which was mounted directly by aufs. The problem is that a subdirectory containing another bind-mount was not carried. So I wonder why aufs can see one bind mount but not another. rbind instead of bind does not help (and could not) as it is aufs that sort of needs to do the rbind action but doesn't seem to have that option. aufs supports layers so maybe I could add the project sources as another RO layer - except aufs splices the layers at the top level and not at a specified subdirectory, and my project source dirs are not top level. For now I may have to splice them at top level and then do a bind mount on top of aufs to put them in the right place in the aufs tree but I don't like it Any tips or hints on how to do this properly with aufs? Sam
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