I am looking for something that would save me the hassle to have to sync various folders. Basically I work with video and photos; I have 2 different folders for each media, and each folder contains more folders with my projects. When I add photos/videos, or modify them, I have to either copy the whole folder in my backup location, or I have to do it manually, looking at what I modified, check date modified, size of the folders and spend time doing the sync. Is there any app (free or not), that would check a folder for changes (every day or so), find if there are changes and copy only what was modified? Without overwrite everything? (one folder has 580 Gb, the other .9 Tb; as you can imagine copy all is not an option). I have tried writing a shell script, but more than once I just blew everything, because for a reason or another a file would lock and not being copied, or the date would not be consistent with the effective modified date and so on, so I am hoping that there is out there something simple that just monitor 2 folders and keep them in sync, preserving the structure and avoiding to copy all every single time. Thanks!