SwitchFS
http://code.google.com/p/sfs

SwitchFS requires FUSE 2.5 or later with relevant kernel support. This is
included with most distributions, however more information may be found at:
http://sourceforge.net/projects/fuse

To run an out-of-source CMake build (recommended):
# mkdir bin
# cd bin
# cmake ../src
# make

To run the test suite:
# make && make test

To set up a sfs mount, create a configuration file containing a space or line
delimited list of source directories (specified by absolute path) where files
are to be stored. Pass the location of this file on the command line while
mounting sfs. See switchfs.conf.example and the example command below.

To mount:
# ./sfs -check -balance -o config=<configuration_file> <mount_dir>

To unmount:
# fusermount -u <mount_dir>

To mount running in the foreground for debugging add the '-d' flag:
# ./sfs -d -check -balance -o config=<configuration_file> <mount_dir>
