How to rsync only new files

From man rsync:

--ignore-existing       skip updating files that exist on receiver

--update does something slightly different, which is probably why you are getting unexpected results (see man rsync):

This forces rsync to skip any files which exist on the destination and have a modified time that is newer than the source file. (If an existing destination file has a modification time equal to the source file's, it will be updated if the sizes are different.)

In my case I had similar issues, having all files transferred instead of only the modified/new ones. I solved this by using parameters -t (instead of -a), and -P (equivalent to --partial --progress):

rsync -h -v -r -P -t source target

This transfers only new files, and files already existing but modified: -a does too much, like user and group ID sync, which in my case can not work as I have different users and groups on my source and target systems.

The parameters in detail:

• -h: human readable numbers
• -v: verbose
• -r: recurse into directories
• -P: --partial (keep partially transferred files) +
          --progress (show progress during transfer)
• -t: preserve modification times