Any suggestion about LFS tuning ?

i got two raid5 (raidframe) device of the same size,the one formatted
with LFS has poor performance (according bonnie) the other
with FFS is far superior..

LFS: (formatted with fsize=8192,bsize=0,sgs=7 according with disklabel
and raid5 stripe 8K)

File './Bonnie.387', size: 104857600
Writing with putc()...done
Rewriting...done
Writing intelligently...done
Reading with getc()...done
Reading intelligently...done
Seeker 1...Seeker 2...Seeker 3...start 'em...done...done...done...
              -------Sequential Output-------- ---Sequential Input--
--Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block---
--Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU 
/sec %CPU
          100  1724  5.1  1741  2.7   787  1.7  1253  3.6  1552  1.2 
33.9  0.5




FFS:(formatted with fsize=8192,bsize=1024,sgs=16 and raid5 stripe 16k)

File './Bonnie.379', size: 104857600
Writing with putc()...done
Rewriting...done
Writing intelligently...done
Reading with getc()...done
Reading intelligently...done
Seeker 1...Seeker 2...Seeker 3...start 'em...done...done...done...
              -------Sequential Output-------- ---Sequential Input--
--Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block---
--Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU 
/sec %CPU
          100  3787  7.5  3851  2.0  1855  1.9 13693 45.2 17068 18.7
112.8  1.4


Another ,not so directly related, question:

why access on a remote file system(nfs) mounted with async option is 
two time faster than access on the same filesistem mounted without async
option?

I'm using NetBSD 1.5.1.

Thanks!