So I'm on the look for a Mac App that would allow me to sync drive, not necessary clone a drive, so let me explain. Say I have a 3TB drive in my MacPro that contains documents, videos and photos, its not an OS boot drive. I'm looking for an app that can backup that 3TB drive into an 3TB external drive and that external drive I want to store away in a safe place. I will still continue to use the 3TB drive in my MacPro to, add or delete as I see fit until, lets say a month as passed and I want to 'sync' the 3TB drive with my external 3TB drive that I had backed up previously. I want to be able to hook up my external drive open an app and let that app 'sync' any changes that have been made on my internal 3TB drive onto my 3TB external drive, then remove the external drive and store it away again for another couple of weeks. Most apps I see I think require the drive to be attached 24/7 which is not what I'm looking for, I actually want to remove the drive and store it until I need to backup again. This way the drive it self doesn't 'wear down' being continuously on. Any recommendations would be very helpful.