mkfs.xfs options with Linux RAID

[AndyLiebman@xxxxxxx]

I have read in a couple of places that, in addition to setting the block size 
with the -b size=XXXX flag, when using xfs under Linux along with RAID, it's 
a good idea to set an xfs option with the -d  flag (is it the suint, the 
swath, or something like that?) so that it's equal to the block size. Can 
somebody 
explain this?  Which is the correct parameter to use? Why should these things 
be equal? And what happens when they're not equal? 

Thanks

Andy Liebman