Parallel rsync Source: http://www.krazyworks.com/making-rsync-faster/

parallel_rsync.sh

#!/bin/bash

# Define source, target, maxdepth and cd to source
source="/tmp/source"
target="/tmp/target"
depth=1
cd "${source}"

# Set the maximum number of concurrent rsync threads
maxthreads=30
# How long to wait before checking the number of rsync threads again
sleeptime=5

# Find all folders in the source directory within the maxdepth level
find . -maxdepth ${depth} -type d | while read dir
do
	# Make sure to ignore the parent folder
	if [ `echo "${dir}" | awk -F'/' '{print NF}'` -gt ${depth} ]
	then
		# Strip leading dot slash
		subfolder=$(echo "${dir}" | sed 's@^./@@g')
		if [ ! -d "${target}/${subfolder}" ]
		then
			# Create destination folder and set ownership and permissions to match source
			mkdir -p "${target}/${subfolder}"
			chown --reference="${source}/${subfolder}" "${target}/${subfolder}"
			chmod --reference="${source}/${subfolder}" "${target}/${subfolder}"
		fi
		# Make sure the number of rsync threads running is below the threshold
		while [ `ps -ef | grep -c [r]sync` -gt ${maxthreads} ]
		do
			echo "Sleeping ${sleeptime} seconds"
			sleep ${sleeptime}
		done
		# Run rsync in background for the current subfolder and move one to the next one
		nohup rsync -a "${source}/${subfolder}/" "${target}/${subfolder}/" </dev/null >/dev/null 2>&1 &
	fi
done

# Find all files above the maxdepth level and rsync them as well
find . -maxdepth ${depth} -type f -print0 | rsync -a --files-from=- --from0 ./ "${target}/"