I ran a couple tests, and I didn't see a 4x difference, but
mtools would usually win. The most dramatic difference I saw
was on a 45 MB file.
mtools: 35.66 seconds to write file.
fat: 87.49 seconds to write file.
So mtools in this case is 2.5x faster than the kernel fat code.
Gordon Chaffee
plateau.cs.berkeley.edu