su,sw suboptions clarification on fs creation

[Dragos Delcea <dragos.delcea@farmexim.ro>]

Hello,

given a recent linux distribution (SuSE 8.1) and a raid 0 logical disk
(hardware raid with stripe=16k) with 3 scsi disks, what are the right
parameters used at fs creation?
I used:

#mkfs.xfs -l logdev=/dev/sda3,size=32768b -d \
su=16384,sw=49152,unwritten=0 /dev/sdb1 -f;

but I have doubts about sw suboption, in the man page of mkfs.xfs the
explanation seemd clear at first, but (I'm not an native english
speaker) the more I stare at it, the more confused I get. Should it be
sw=(su*number_of_disks)=49152, or sw=number_of_disks=3?

also, does "unwritten=0" helps performance?
the fs will be used for some datafiles of an oracle test instance (few 
files, but big ones).

thanks,
dragos