Compressed Read-Write Filesystems in Linux:

(most of the commonly-used compressed FS'es are read-only)

Reiser4 provides compression but it's development and future is uncertain:  http://en.wikipedia.org/wiki/Reiser4#Future_of_Reiser4

gzipfs doesn't have much documentation:

• http://ole.tange.dk/projekter/fri-software/fist.html
• http://www.fsl.cs.sunysb.edu/docs/zadok-thesis-proposal/node94.html

btrfs looks interesting (and has been suggested as a replacement for those formerly interested in Reiser4) and is in active development but is not ready for production use:  http://btrfs.wiki.kernel.org/index.php/Main_Page .     And more info here.


jffs2 might be an option:  http://en.wikipedia.org/wiki/JFFS2     (don't know if it works on hard drives)

There's a patch (ext2comp) for ext2/ext3, but I'd rather an out-of-the-box solution.

compFUSEd and FuseCompress are mentioned often, but don't seem to be production-quality products and development doesn't seem to be very active anymore.