I have long had two hard drives and a Mirror RAID set-up. All functions in the background whenever I mouse on the save icon. It has saved my bacon several times cos HD's fail. But I have had more grief from the wretched Promise Raid Controller than I care to dwell on, repeatedly having to rebuild the array. Yeh, not so very hard but terrybull tedious.
I finally ditched twin HD and the Promise RAID controller and now use a single internal HD and save as&when to an external hard drive. Perhaps not an ideal solution but less tedious than Mirror RAID.
Obscurity is a comfortable cloak