This message was posted on behalf of Intel Corporation
Thank you for reaching out, I've reviewed your question and as it is right now, Raid technology does not support Online Capacity Expansion in spanned arrays such as RAID 10, RAID 50, or RAID 60.
However, as a work around it is possible to back up the data, create a new array with all the drives and restore the data to the new array afterwards, it takes a little longer but it does the trick.
For further reference please check:
How to Perform Online Capacity Expansion (OCE) Using the Intel® RAID Web Console 2 Utility for Hardware Intel® RAID Controllers
I hope this answer your question if so or if you need anything else please let me know, I'll stay tuned to your comments.
Intel Customer Support