SATA is slow plus your array could be busy with other more important things.
i got some RGs that i would like to expand instead of creating a new raid group. The available disks are mix of sata and fc.   to expand the rg, I can just right click on the rg and go to disk and pick the disk i want then expand right?  Is there a problem with this or is there a better way? 
expanding a raid group with existing disks