I've been to these forums many times to search for and get answers, but now I'm a bit stuck and need help. Let me first provide some context for my question. I am a writer and author, and plan to move from an early 2009 iMac to a MacBook Pro Retina. I plan to use it as a desktop with an external monitor and keyboard and have the benefit of occassional using it as a portable on it's own. The storage space is more limited than on my iMac. Therefore, I'm planning to have a lot of my files such as photos etc on the external drive and probably have some of my documents stored on it as well. Given that my writing is my living, I am paranoid about losing data. I currently back up to an external drive that I use for Time Machine, and also using other means back up to two additional external drives. In addition my writing backsup to cloud storage. This may seem a bit paranoid but I did have the experience a few years back where the drive failed on my Mac AND the external drive failed. So now I take care because a loss could mean losing years of reasearch and work. So, my question is, with now files being stored off on an external drive, is there software that will automatically synch, back up or replicate one external drive to another, so I can have complete redundancy? This would be in addition and supplemental to backing on on a drive reserved for Time Machine. Thanks!