Incremental BTRFS backups

btrfs-backup.sh

#!/bin/bash

#
# Sync data using rsync to a backup BTRFS fs subvolume and create
# incremental revolving snapshots
#
# Setting the -c option will setup crontab to continue running the
# backup at the set granularity (default daily)
# 
# Install:
#
# cd /usr/local/bin
# wget https://gist.github.com/raw/970260/btrfs-backup.sh
# chmod 755 btrfs-backup.sh
#
# Show usage:
#
# btrfs-backup.sh -h
#

usage {
cat << EOF
usage: $0 [options] /path/to/backup /path/to/btrfs/volume subvol-name

Run / setup incremental backups to a BTRFS volume

OPTIONS:
   -h      Show this message
   -g      Granularity for increments. OPTIONS: hour, day, week, month DEFAULT: day. Use with -c will setup an appropriate crontab
   -i      Number of increments to save. DEFAULT: 7. -g hour -i 24 would save 24 hourly snapshots before overwriting old snapshots
   -c      Setup crontab job with current settings
   -l      Log file to append backup/snapshot log to.
   -s      Sleep mode. Unmount and put the BTRFS device to sleep after backup. Requires the volume to be setup in /etc/fstab
   -v      Verbose rsync
EOF
}

DX=day
INC=7
CRON=false
SUBVOL=
LOG=
SLEEP=
VERBOSE=">/dev/null"
while getopts “hcvsg:i:l:” OPTION
do
     case $OPTION in
         h)
             usage
             exit 1
             ;;
         c)
             CRON=true
             ;;
         v)
             VERBOSE=""
             ;;
         s)
             SLEEP=true
             ;;
         g)
             DX=$OPTARG
             ;;
         i)
             INC=$OPTARG
             ;;
         l)
             LOG=$OPTARG
             ;;
         ?)
             usage
             exit
             ;;
     esac
done

if [ -z "$1" ] || [ -z "$2" ] || [ -z "$3" ]; then
  usage
  exit 1
fi

function snapshot {
  # delete old snapshot
  if [ -d $1/$2-$3 ]
  then
    btrfsctl -D $2-$3 $1 $VERBOSE
  fi

  btrfsctl -s $1/$2-$3 $1/$2 $VERBOSE

  if [ ! -z "$LOG" ]; then
    echo "snapshot $2-$3: `date`" >> $LOG
  fi
}

# find the appropriate absolute timestamp depending on granularity. day=daystamp, hour=hourstamp etc
# timestamp forever increase with time so are useful for ensuring increments can loop over each other
case $DX in
  hour)
    dx=60*60
    ;;
  day)
    dx=60*60*24
    ;;
  week)
    dx=60*60*24*7
    ;;
  ?)
    echo "Invalid granularity, only hour, day, week are supported"
    exit 1
    ;;
esac

# If sleep is specified, try and mount the volume first.
# Otherwise it should already be mounted
$SLEEP &&
  #setup sleep
  (mount $2 &&
   DEV=`mount | grep "$2 type btrfs" | awk '{print $1}'`) ||
  # without sleep
  (test -d $2/$3 &&
   mount | grep "$2 type btrfs" >/dev/null)

if [ $? -ne 1 ]; then
  $SLEEP &&
    echo "Unable to mount BTRFS volume or it does not appear to be BTRFS. Make sure it is setup in /etc/fstab" ||
    echo "$2 does not appear to be a mounted BTRFS volume. It must be the parent BTRFS volume and not a subvolume. Use -s to set subvolumes"
  exit 1
fi

if [ ! -d $1 ] && [ ! -f $1 ]; then
  echo "$1 does not exist"
fi

# rsync into BTRFS volume
rsync -va --progress --numeric-ids --delete-before --ignore-errors --partial --inplace --sparse $1/ $2/${3/%\//} $VERBOSE

# the granularity-adjusted timestamp value
((ts=`date +%s`/$dx))

# snapshot dir
# TODO provide option to save snapshots into a different directory
((num=$ts%$INC))
snapshot $2 $3 $num

# unmount and put to sleep
$SLEEP &&
  umount $2 $&&
  hdparm -Y $DEV $VERBOSE

# setup a crontab entry for this backup job
if $CRON; then
  [ $DX == "hour" ] && HOUR="*" || HOUR="0"
  [ $DX == "week" ] && WEEK="0" || WEEK="*"
  CMD="$0 -g $DX -i $INC `[ ! -z "$LOG ] && echo "-l $LOG"` `$SLEEP && echo "-s"` $1 $2 $3"
  echo "`crontab -l`"$'\n'"0 $HOUR * * $WEEK $CMD" | crontab
fi