#!/bin/bash
# run 20 file copy streams at one time, in parallel
# good approach for larger files
cnt=0
find /path/to/files -type f |
while read fname do
    scp $fname  username@server_ip:/path_to_remote_directory
   cnt=$((  $cnt + 1  ))
   if [  $((  $cnt % 20   )) -eq 0 ] ; then
      wait
  fi
done