I'm in the process of upgrading to a Retina MBP, and with the 256 GB hard drive, I'm going to have to make an effort to focus on using a couple of external drives as part of my normal workflow. Until T-bolt externals come down in price, I'm going to go with a couple of USB 3.0 capable 3 TB externals. My question is: Are there any programs out there that will automatically copy files to the 2nd external after I move files onto the first? Ideally, I will only work with files on one of them, with the changes being backed up to the 2nd automatically. Any input is appreciated.