Safer (also known as SFK) 128 is claimed to be as strong as triple DES,
it is public domain and is fast. It's main drawback is that it is a
block rather than stream cipher, it will only handle data in chunks of
8 bytes. If the filesystem blocks are a multiple of 8 bytes and you
encrypt filesystem blocks rather than filesystem data then you should
have no problems.
ftp://ftp.isi.ee.ethz.ch/pub/simpl/safer.V1.2.tar.Z