@Geldorn: Thanks for that. I don't have MGS4, or I might've done the same thing with my Gentoo installation on my PS3.
One thing though, does your fiile manager report 'MSG' as being 27.2GB in size? I may have added it up wrong, but the 2gigs of random files plus the *.dat files only appear to be about 10 gigs.
If there is a discrepancy, could the rest of the files be stored in some funky non-standard file system on the disk?