Conclusion

Aufs easily creates workarounds to provide virtual write access to read-only media or files residing in read-only filesystems, such as ISO9660 (which supports no write operation, whether the underlying block device is writable or not). Without aufs, then symlinks, bind-mounts, and filesystem restructuring is necessary to support writing to otherwise unwritable files. Setting up a chroot environment to record changes to the filesystem is easy with aufs, because it puts all changed files and a record of modifications to metadata on the writable branch. With this feature, you can create "incremental" installations by adding filesystem history step by step. Also, you can use existing mount points as targets, so the old directory data is "hidden" by the modified data.

Aufs2 users have long backed adding aufs2 to the main kernel. Because of attempts to add overlay capabilities into the generic virtual filesystem layer rather than a separate filesystem, aufs2 likely won't make it into the kernel soon.