sorry again, the last interesting thing (that i remember)

compression is a nice feature, check this:
https://btrfs.wiki.kernel.org/index.php/Main_Page   (BTRFS may online
compress files, i don't know if it's stable)

http://en.wikipedia.org/wiki/JFS_(file_system)    (JFS version 1, but
i don't know if you will have bugs)

https://code.google.com/p/fusecompress/         (FUSE is a userland
filesystem tool, maybe not too fast as a kernel land filesystem, but
it do a nice job)
http://squashfs.sourceforge.net/                       (read-only filesystem)

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