I work in an office where we have two Macs with Adobe Production Suite. They each have a 4TB external drive and we want to keep them synced bi-directional. The reason is for two reasons: backup, but also so we can easily access a project from our own terminal if the other user is out. So I'm looking for a good piece of software that can keep the two drives in sync either on a schedule or when it senses the file structure has changed. Can anyone recommend such a program?