Aufs mount alternative What union mounts are available on OSX? I've been using Aufs on Ubuntu for the past few years without fail and I'm looking for something similar...

Basically, given n directories, merge the contents into another directory in real-time. Any changes to the mount directory does not affect the original paths, and the changes that were made are put into the furthest left path. This allows me to create a complex working directory of several repositories, while maintaining the history and integrity of those directories cleanly.

Example:

mount -t aufs -o br=/src1:/src2:/src3 none /path/to/stacked/dir


Would combine src1, src2 and src3 into /path/to/stacked/dir
You can use the union option available in OSX's mount:

sudo mount -t hfs -o union /dev/disk9s1 /tmp/union

See also: http://osxbook.com/book/bonus/ancient/whatismacosx/arch_fs.html