Hi, I am not sure how this can be done. and I am not sure if RAID provide a solution to this. I have two identical 500G SATA to USB HD. I would like to find a way to make them appear to be a 1T HD in Mountain Lion. I know Disk Util has some basic functions to set them up as RAID, but , it doesn't seem to be the right solution. All I want is for the two drivers appear to be one and back up my data. Any suggestions? Thanks in advance.