Can you see how lfs and fat perform, in comparison for ffs?

I could, but I don't have spare time and this is a production server.

I have no idea why would anyone want to use FAT.

LFS is interesting, but I'd expect the large file to get fragmented as
the domU does block IO.  And I don't have a warm fuzzy that it's
completely stable and reliable, which is more important than speed.

-- 
        Greg Troxel <gdt@ir.bbn.com>