Quickest efficient backup software - External to External
 

I am backing up files on 2 external hard drives with about 3TB of data on each. I am looking for an efficient software out there that will backup new and modified files to the other drive on demand without having to copy over all the files taking hours.

Any recommendations would be greatly appreciated. Right now I am simply copying and pasting but it is time consuming especially if I reorganize the files on one drive.

Also well I am at it, does anyone know of a software that will remove duplicate files? Even if they have the same name or at least if they have a specific keyword in it like "copy"

bumpity bump

goodsync is very handy for windows
backuppc for linux