Configure two partitions (one currently in use) to work as RAID1.

05-create_root_raid_pass1.sh

#!/bin/bash -e
#
# Goal:
# Configure two partitions (one currently in use) to work as RAID1.
#
# Inspiration:
# http://blog.drewwithers.com/2013/11/raspberry-pi-usb-raid1-root-partition.html
# https://wiki.archlinux.org/index.php/Convert_a_single_drive_system_to_RAID
#
# Prerequisites:
# 1. Run 04-configure_initramfs.
# 2. Set the following variables:
#
FIRST_SD_CARD=/dev/mmcblk0
#FIRST_BOOT_PARTITION=${FIRST_SD_CARD}p1
FIRST_ROOT_PARTITION=${FIRST_SD_CARD}p2
#FIRST_APP_PARTITION=${FIRST_SD_CARD}p3
SECOND_SD_CARD=/dev/sda
#SECOND_BOOT_PARTITION=${SECOND_SD_CARD}1
SECOND_ROOT_PARTITION=${SECOND_SD_CARD}2
#SECOND_APP_PARTITION=${SECOND_SD_CARD}3
ARRAY=/dev/md
# BOOT cannot be RAIDed
ROOT_ARRAY=${ARRAY}2
#APP_ARRAY=${ARRAY}3

echo "Are we superuser?"
[[ $EUID -eq 0 ]]
echo "OK"

echo "Are we running on the rPi?"
[[ "$(uname --machine)" == arm* ]]
echo "OK"

echo "Are we running from the primary partition $FIRST_ROOT_PARTITION?"
df --exclude=tmpfs | awk -v PATTERN="$FIRST_ROOT_PARTITION" '$6 == "/" { if($1 != PATTERN) exit 1 }'
# --exclude-type to shorten list
# -v to pass FIRST_ROOT_PARTITION from bash into awk script
# $6 == "/" find the root partition and if it is not mounted to FIRST_ROOT_PARTITION exit with error
echo "OK"

echo "Is card $SECOND_SD_CARD plugged in?"
[[ -e "$SECOND_SD_CARD" ]]
echo "OK"

echo "Does partition $SECOND_ROOT_PARTITION exist?"
[[ -e "$SECOND_ROOT_PARTITION" ]]
echo "OK"

# need to install stuff, so:
apt-get update

echo "Install and configure mdadm."
printf "mdadm\tmdadm/initrdstart\tstring\tall" | debconf-set-selections
apt-get -qq install mdadm
echo "OK"

echo "Create degraded RAID."
mdadm --zero-superblock "$SECOND_ROOT_PARTITION"
mdadm --create "$ROOT_ARRAY" --run --level=1 --raid-devices=2 "missing" "$SECOND_ROOT_PARTITION"
printf "ARRAY\t$ROOT_ARRAY\tname=$(hostname):2\n" >> /etc/mdadm/mdadm.conf
echo "OK"

echo "Format array $ROOT_ARRAY."
mkfs.ext2 -L "root" "$ROOT_ARRAY"
echo "OK"

echo "Copy live system over to RAID."
echo "There is no progress indicator, and this could run for several minutes."
apt-get -qq install rsync
ROOT_MOUNT=/tmp/root
mkdir --parents "$ROOT_MOUNT"
mount "$ROOT_ARRAY" "$ROOT_MOUNT"
rsync --archive --acls --xattrs --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found","/boot/*","/app/*"} / "$ROOT_MOUNT"
echo "OK"

echo "Modify fstab on array $ROOT_ARRAY."
#TODO: this makes assumptions I am not sure I am confortable with
sed --in-place 's/mmcblk0p2/md2/' "$ROOT_MOUNT/etc/fstab"
sed --in-place 's/ext4/ext2/' "$ROOT_MOUNT/etc/fstab"
echo "OK"

echo "Configure boot parameters in cmdline.txt."
#TODO: this makes assumptions I am not sure I am confortable with
sed --in-place 's/mmcblk0p2/md2/' "/boot/cmdline.txt"
sed --in-place 's/ext4/ext2/' "/boot/cmdline.txt"
sed --in-place 's/rootwait/boot_delay=20 rootdelay=10 rootwait/' "/boot/cmdline.txt"
echo "OK"

echo "Requires reboot."
read -n1 -r -p "Press any key to continue, Ctrl-C to abort..." ignore
reboot
echo "Done."