SyncDir is one way synchronization tool for directories or files. It is java based, simple command-line utility. Synchronize a specified target directory or file to match a specified source directory or file. Only the target is modified. Flexible file-matching: combinations of name, size, time, CRC. Computing CRC can be time consuming, so if one is sure, that other characteristic are defining files well enough, could be ommited. Here is an example of command line for regular backup Documents directory to the USB disk at D:
java -jar "C:\\Java\\Sync\\sync.jar" --nocrc --exclude:"Thumbs.db,~*" C:\\Users\\JoeDoe\\Documents D:\\Arc-Docs