Time Machine backup snapshotting on ZFS using zrepl for snapshot purging (for Samba server)

timemachine-zfs-snapshot

# /etc/cron.d/samba-timemachine-zfs-snapshot

# Create snapshots after completed Time Machine backups.
# Runs every two minutes to allow creating backups only after cleanup is
# completed.
*/2 * * * * root /usr/local/bin/timemachine-zfs-snapshot.sh rpool/share/timemachine

timemachine-zfs-snapshot.sh

#!/usr/bin/env zsh
# /usr/local/bin/timemachine-zfs-snapshot.sh
setopt err_exit

PATH=/sbin:$PATH
DATASET=$1

# Custom logic for detecting when a client completed a Time Machine backup,
# we're not relying on Samba user disconnect scripts because Time Machine
# often leaves the connection open indefinitely.
#
# Dataset structure is [dataset]/[user], inside each user dataset there is
# expected to be only one device backup, multiple devices under a user may
# create snapshots at a point where one machines backup is incomplete.
for dir in $(zfs get mountpoint -o value -H $DATASET)/*; do
	user=${dir:t}
	for bundle in $dir/*.backupbundle; do
		# Files must exist, Results for instance is present only after first completed backup.
		if [[ ! -f $bundle/com.apple.TimeMachine.Results.plist ]] || [[ ! -f $bundle/com.apple.TimeMachine.SnapshotHistory.plist ]]; then
			continue
		fi

		# Avoid creating backup before cleanup has been performed.
		if (( $(stat -c '%Z' $bundle/com.apple.TimeMachine.Results.plist) < $(stat -c '%Z' $bundle/com.apple.TimeMachine.SnapshotHistory.plist) )); then
			continue
		fi

		latest=$(grep -A1 com.apple.backupd.SnapshotCompletionDate $bundle/com.apple.TimeMachine.SnapshotHistory.plist | tail -n1 | cut -d'>' -f2 | cut -d'<' -f1 | tr T _ | cut -d: -f1-3 | tr -d : | tr -d Z | tr -d -)
		latest=tm_${latest}_000  # zrepl prefix and standard timestamp suffix.
		if zfs list -t snap -H $DATASET/$user@$latest 1>/dev/null 2>&1; then
			continue
		fi

		# Time Machine can keep modifying files for a while after completion.
		if (( $(find $bundle \( -mmin -3 -o -cmin -3 \) -print -quit | wc -l) > 0 )); then
			continue
		fi

		zfs snap $DATASET/$user@$latest
	done
done

# Trigger zrepl snapshot pruning and replication.
zrepl signal wakeup timemachine

zrepl.yml

# /etc/zrepl/zrepl.yml
jobs:
  - name: timemachine
    type: snap
    filesystems:
      "rpool/share/timemachine<": true
      "rpool/share/timemachine": false
    snapshotting:
      type: manual
    pruning:
      keep:
        - type: last_n
          count: 15
          regex: "^tm_.*"
        - type: grid
          grid: 7x1d | 2x1w
          regex: "^tm_.*"