#!/bin/bash

echo "Please read the script first, and comment the exit line at the top."
echo "This script will require about 3MB of free space, it will free (and use)"
echo "loop devices 1 2 and 3, and will use the md device number specified in MD_DEV."
exit 0

MD_DEV="md9"    # make sure this is not an array you use
COMP_NUM=3
COMP_SIZE=$((1 * 1024 * 1024 + 8192))     #1MiB comp sizes with room for 8k (16 sect) of metadata

mdadm -S /dev/$MD_DEV &>/dev/null

DEVS=""
for i in $(seq $COMP_NUM); do
    echo -n "Creating component $i ($COMP_SIZE bytes)... "
    losetup -d /dev/loop${i} &>/dev/null
    
    set -e
    PCMD="print \"\\x${i}${i}\" x $COMP_SIZE"   # fill entire image with the component number (0xiiiiiii...)
    perl -e "$PCMD" > dummy${i}.img
    losetup /dev/loop${i} dummy${i}.img
    DEVS="$DEVS /dev/loop${i}"
    set +e
    echo "done."
done

echo
echo
echo "==============================================================="
echo "Creating $COMP_NUM disk raid5 array with v1.1 superblock"
# superblock at beginning of blockdev guarantees that it will overlap with real data, not with parity
mdadm -C /dev/$MD_DEV -l 5 -n $COMP_NUM -e 1.1 $DEVS

echo -n "Waiting for resync to finish..."
while [ $(cat /sys/block/$MD_DEV/md/sync_action) != "idle" ] ; do
    echo -n "."
    sleep 1
done
echo " done."
echo
grep -A1 $MD_DEV /proc/mdstat 

echo
echo -n "Initial checksum of raw raid5 device: "
md5sum /dev/$MD_DEV

echo
echo
echo "==============================================================="
echo "Failing first componnent"
mdadm -f /dev/$MD_DEV /dev/loop1
mdadm -r /dev/$MD_DEV /dev/loop1

echo
grep -A1 $MD_DEV /proc/mdstat 

echo
echo -n "Checksum of raw raid5 device after failing componnent: "
md5sum /dev/$MD_DEV

echo
echo
echo "==============================================================="
NEWSIZE=$(( $COMP_SIZE - $(cat /sys/block/$MD_DEV/md/rd1/offset) * 512 ))
echo "Re-creating block device with size $NEWSIZE bytes, so both the superblock and data start at the same spot"
losetup -d /dev/loop1 &>/dev/null
PCMD="print \"\\x11\" x $NEWSIZE"
perl -e "$PCMD" > dummy1.img
losetup /dev/loop1 dummy1.img

echo "Adding back to array"
mdadm -a /dev/$MD_DEV /dev/loop1

echo -n "Waiting for resync to finish..."
while [ $(cat /sys/block/$MD_DEV/md/sync_action) != "idle" ] ; do
    echo -n "."
    sleep 1
done
echo " done."

echo
grep -A1 $MD_DEV /proc/mdstat 

echo
echo -n "Checksum of raw raid5 device after adding back smaller component: "
md5sum /dev/$MD_DEV

echo
echo 
echo "==============================================================="
echo "Attempting recovery"
echo repair > /sys/block/$MD_DEV/md/sync_action
echo -n "Waiting for recovery to finish..."
while [ $(cat /sys/block/$MD_DEV/md/sync_action) != "idle" ] ; do
    echo -n "."
    sleep 1
done
echo " done."

echo "Performing check"
echo check > /sys/block/$MD_DEV/md/sync_action
echo -n "Waiting for check to finish..."
while [ $(cat /sys/block/$MD_DEV/md/sync_action) != "idle" ] ; do
    echo -n "."
    sleep 1
done
echo " done."

echo
echo -n "Current value of mismatch_cnt: "
cat /sys/block/$MD_DEV/md/mismatch_cnt

echo
echo -n "Checksum of raw raid5 device after repair/check: "
md5sum /dev/$MD_DEV