I just got an OWC Mercury Elite RAID unit that can store two hard drives in RAID or independent modes. The purpose is to store my old video projects for long term storage and other media backup. The drives are WD Caviar Greens with the same model ID: WD20EARS (not the newest model, but from a couple years ago). This is my first time to use RAID storage of any sort. The plan is to put both of them in the Elite and then put my old projects and media on them. Originally, I planned to use RAID1, which is the mirror setup and can rebuild if one drive fails. However, from what I read, it is highly recommended to use the same model HDD, which I am, but I worry about what happens when a drive fails and I need to replace it and the WD20EARS are no longer made. How important is it to have identical model HDDs? If one fails, is it okay to replace it with, say the newer model of the Caviar Green? If having a different HDD model will screw up the RAID, then would it be better to set up the Elite in "independent" mode, which shows both drives as separate volumes? Then I would manually duplicate the data on both drives and if one fails, I can put in a newer and/or larger capacity HDD and manually duplicate the data over from the existing HDD. What would be best?