Proper SU/SW values for nested raids RAID50/RAID60

["Mark Noon" <mnoon@xxxxxxx>]

I'm trying to understand the proper values when formatting an xfs filesystem under a hardware raid controller and seem to get conflicting information between whats on the wiki and various mailing listings and forum posts when searching google. I have a system that will be storing images and other static content files accross a RAID50. The plan is to do 3 raid5 arrays each with 5 disks with a stripe size of 128K striped accross a raid0. I will then build a logical volume on top of this.

 

When running mkfs.xfs should the correct settings be su=128k sw=12 (-1 parity 'disk' for each of the 3 arrays) or su=128k sw=4 (only consider one of the arrays)? 

 

Also if I ever add a JBOD and extend the storage how does this change things esspecially given that it will be on a completely different raid volume just merged together via LVM?

 

Thanks for the assitance!