Persistent ramdisk with tmpfs and rsync

#!/bin/bash

# QUESTIONG: What's the purpose of this script?
# ANSWER: 
# The purpose is to mount a part of the computers RAM to a folder on the harddrive.
# This will make IO to that folder VERY fast. However the content of such a folder
# will be erased on system restart. This script uses rsync to mirror the content of
# another folder on the harddrive. This way the persistance issue is solved as well

# QUESTIONG: How do I use this script?
# ANSWER: 
# Make sure this script runs 
#  - directly after system start
#  - directly before system shutdown
#  - every once in a while
#
# You whould not care about the hdd-folder (on the hard-drive).
# Work with the files in the ram-folder. This script will take care of the save and
# load to hdd. See the hdd-folder as a persistance backup you don't need to care about :)

# QUESTION: How do I install this? 
# QUESTION: Where should I put this script?
# QUESTION: How do I make it execute at those times you mentioned above?
# ANSWER: (For Ubuntu)
# Put this script here: /etc/init.d/ramdrivetick
# Then run this: chmod +x /etc/init.d/ramdrivetick
# Then run this: update-rc.d ramdrivetick defaults
# The script will now run on startup, reboot and shutdown.
# To make it run each other create a file /etc/cron.hourly/runramdrivetick with this content
# ---------
# #!/bin/bash
# . /etc/init.d/ramdrivetick
# ---------
# Then run this: chmod +x /etc/cron.hourly/runramdrivetick
# If you get this message: /bin/bash^M: bad interpreter: No such file or directory
# This means that you have incorrect line endings in the file. Make them linux line endings.

# QUESTION: How do I uninstall this? 
# Run this: rm /etc/cron.hourly/runramdrivetick
# Run this: update-rc.d -f ramdrivetick remove

# QUESTION: How can I trigger a manual "tick"?
# Run this: service ramdrivetick

# ===== Configuration START =====
SIZE="4000m" #Size of the RAM folder. This obviously can not be more than the RAM available on your system.
FOLDER_RAM="/ramdrive" # Path to the folder where the ram will be mounted
FOLDER_HDD="/ramdrivehdd" # Path to our backup hdd folder
PERMMODE="0755" # The permission for the folders. Used when creating non-existing folders and when mounting.
MARKFILE_INITIATED=".zz_ramdrive_initiated" # This file is used to mark if the initial move of items from hdd to ramdisk yet is done
MARKFILE_RUNNING=".zz_ramdrive_sync_is_running" # Marking that an action is running at the moment.
# ===== Configuration END =====

# Calculate folderpaths for the markers
MARKFILE_INITIATED_FOLDER="${FOLDER_RAM}/${MARKFILE_INITIATED}"
MARKFILE_RUNNING_FOLDER="${FOLDER_RAM}/${MARKFILE_RUNNING}"

# ===== Function Declarations START =====
func_sayhi()
{
	echo ""
	echo "====== RamDriveTick START ======"
}

func_exit()
{
	echo "====== RamDriveTick END ======"
	exit 0
}

func_mark_open()
{
	# Stop if a sync is running already
	if [ -e "${MARKFILE_RUNNING_FOLDER}" ]; then
		echo "A sync is already in progress. Exiting."
		func_exit
	fi
	# Otherwise mark this sync in progress
	touch ${MARKFILE_RUNNING_FOLDER}
}

func_mark_close()
{
	rm ${MARKFILE_RUNNING_FOLDER}
}

func_makefolders()
{
	# Create the folders if they don't exist :)
	if [ ! -d "${FOLDER_HDD}" ]; then
		echo "Creating hdd folder \"${FOLDER_HDD}\""
		mkdir -p ${FOLDER_HDD}
		chmod ${PERMMODE} ${FOLDER_HDD}
	fi
	if [ ! -d "${FOLDER_RAM}" ]; then
		echo "Creating ram folder \"${FOLDER_RAM}\""
		mkdir -p ${FOLDER_RAM}
		chmod ${PERMMODE} ${FOLDER_RAM}
	fi
}

func_mount()
{
	# Mount the tmpfs if it isn't already mounted
	if ! mountpoint -q "${FOLDER_RAM}"; then
		echo "Mounting a tmpfs with size ${SIZE} to the ram mountpoint folder \"${FOLDER_RAM}\"."
		mount -t tmpfs -o size=${SIZE},mode=${PERMMODE} tmpfs ${FOLDER_RAM}
	fi
}

func_sync()
{
	# Syncronize
	if [ -e "${MARKFILE_INITIATED_FOLDER}" ]; then
		echo "Saving from memory to disk."
		rsync -av --delete --exclude ${MARKFILE_INITIATED} --exclude ${MARKFILE_RUNNING} "${FOLDER_RAM}/" ${FOLDER_HDD}
	else
		echo "INIT! The ram drive content will now be synchronized to look like the hdd content."
		rsync -av "${FOLDER_HDD}/" ${FOLDER_RAM}
		touch ${MARKFILE_INITIATED_FOLDER}
	fi
}
# ===== Function Declarations END =====

# ===== Execute START =====
func_sayhi
func_makefolders
func_mount
func_mark_open
func_sync
func_mark_close
func_exit
# ===== Execute END =====