sunit, swidth question - mkfs.xfs tuning

[Joshua Schmidlkofer <joshua@xxxxxxxxxxx>]

Howdy,
  WOO HOOO!! On 2.4 inclusion, BTW. (good going!)

An old e-mail from Christian Guggenberger recommends swidth be (n-1)
disks for RAID5.  Is that correct?  I have a 66GB volume so I was
looking at:

Mylex AcceleRAID 170, 6 disks in a RAID 5. (4GB system memory)

mkfs.xfs -d su=64k,sw=5 -l size=32m,sunit=64k -L "data"  /dev/...


Is this correct?  Is 32mb a good journal size? This is a mail server,
lots of small files, do I need to optimize the inode options?  I don't
quite understand the full impact of performance here.

thanks,
  Joshua