lessfs

open source alternative to dedup
tried installing it on Centos 5.3, will not work do to kernel version (lower version)
required kernel version is 2.6.26 (I believe)

Prerequisites
FUSE (http://fuse.sourceforge.net/)
Tokyo Cabinet (http://1978th.net/tokyocabinet/)
lessfs (http://www.lessfs.com/wordpress/)

Steps

Fuse
Download from http://sourceforge.net/projects/fuse/files/fuse-2.X/2.8.0/fuse-2.8.0.tar.gz/download
tar xvfz fuse2.8.0.tar.gz
cd fuse2.8.0
./configure
make && make install

Tokyo Cabinet
Download from http://1978th.net/tokyocabinet/tokyocabinet-1.4.36.tar.gz
tar xvfz tokyocabinet-1.4.36.ta.gz
cd tokyocabinet-1.4.36
./configure
make && make install

lessfs
Download from http://sourceforge.net/projects/lessfs/files/lessfs/lessfs-0.8.0/lessfs-0.8.0.tar.gz/download
tar xvfz lessfs-0.8.0.tar.gz
cd lessfs-0.8.0
set env variables
export PKG_CONFIG=/usr/local/lib/pkgconfig
export PATH=/usr/local/bin:/usr/local/sbin:${PATH}
export LD_LIBRARY_PATH=/usr/lib:/usr/local/lib
./configure --enable-off64 (to enable the database limit to >2GB)
make && make install

again like mentioned in the 2nd line above, don't have any centos or rhel with kernel 2.6.26, so to be continued....