Delete all data on all the HDs and create a RAID0+1 array.
If using the Intel Matrix program, open up the app and there should be a setting for it. However, I would rather create an image and do it myself. If the something goes wrong, your data will probably be corrupted.
Actually.... if this is only data.... why RAID0+1 at all? You don't need performance to get data off the drives faster.