So you want to increase the space available Intel onboard raid 1 array but you have added some replacement drives of a larger type and you could not find out how to increase the volume size when you added larger disks.
Not so long ago if you wanted to increase the capacity on your raid 1 drive sets you would have had a bit of a stuggle on you hands to the point that you would be putting you data at risk.
The resolution to this problem has been updated through Intel Storage Manager 8.5. If you are using an older version of Intel Storage Manager than 8.5 you are missing an option when you modify the volume again that allows you to extend and utilize 100% of the available space if you have larger drives installed in you array.
Simply upgrade to 8.5, and modify the volume that you converted. Through the wizard where it asks you to select the RAID type, there is a checkbox asking whether you want to utilize the available space. It will allocate the available space and keep your data intact.