what are people's set up for having an external hdd with a low capacity ssd...? ordered a retina iMac 5K with 256 gb. i'm looking for something affordable, given i'm already over budget with this thing. i was thinking the wd my duo usb 3.0... and from my understanding... one of the drives acts as an external hdd for storing media, while the other drive acts as a time machine backup. is this correct? does the time machine backup also backup whats on the internal ssd? i read somewhere that RAID1 is actually just mirroring the other external drive... so does that mean my internal ssd will not be backed up? i'm new at external drives/backup solutions and trying to figure out what the best solution is... without hurting my wallet too much.