Rotera ZFS snapshots i FreeBSD

Denna guide beskriver hur man automatiskt roterar snapshots på ZFS system.

Snapshot skript

Ny version av skriptet som inte kör rename för att rotera snapshots:en:

#!/bin/sh

usage() {
  cat <<EOF
usage: ${0##*/} <label>
  Rotates filesystem snapshots.  If filesystem has the property
  org.freebsd:snap:<label>=<count>, <count> snapshots will be kept
  until the oldest is destroyed when a new one is created.
  The snapshots are named <label>-<timestamp>, where <timestamp>
  is the UTC time in seconds.
EOF
  exit
}

# Default values
: ${PROP:=org.freebsd:snap}

# Parse command line
[ ${#} -ne 1 ] && usage
label=${1}

zfs_destroy_snapshot() {
  # Delete $1 only if classified as snapshot
  [ "$(zfs get -Ho value type "$1" 2>/dev/null)" = "snapshot" ] && zfs destroy "$1"
}

# Iterate over all filesystems with ${PROP}:${label} > 0
zfs list -Ho name,${PROP}:${label} -t filesystem | \
while read name value; do
  [ $value -gt 0 ] 2>/dev/null || continue

  # Iterate over all snapshots, sorted in descending creation order
  # count all matching names, and start delete snapshots
  # when we have reached the limit acoording to the snapshot
  # property
  counter=0
  zfs list -t snapshot -r -d 1 -Ho name,creation -S creation $name | \
  while read snapshot date; do
    if echo $snapshot | grep -q "@${label}" ; then
      counter=$(($counter + 1))
      # If limit is reached, then start delete older snapshots
      if [ $counter -ge $value ]; then
        zfs_destroy_snapshot "${snapshot}"
      fi
    fi
  done
  # Create a new snapshot
  new_snap="${name}@${label}-"$(date "+%Y-%m-%d-%H:%M")
  zfs snapshot "${new_snap}"
done

Skapa följande skript och spara som /root/bin/zfs-autosnap.sh:

#!/bin/sh

usage() {
  cat <<EOF
usage: ${0##*/} <label>
  Rotates filesystem snapshots.  If filesystem has the property
  org.freebsd:snap:<label>=<count>, increments all existing snapshots labeled
  <label>.<num> and creates a new snapshot called <label>.0.  Destroys snapshot
  numbered <label>.<count>.
EOF
  exit
}

# Default values
: ${PROP:=org.freebsd:snap}

# Parse command line
[ ${#} -ne 1 ] && usage
label=${1}

issnap() {
  [ "$(/sbin/zfs get -Ho value type "$1" 2>/dev/null)" = "snapshot" ]
}

# Iterate over all filesystems with ${PROP}:${label} > 0
/sbin/zfs list -Ho name,${PROP}:${label} -t filesystem | \
while read name value; do
  [ $value -gt 0 ] 2>/dev/null || continue

  # Destroy the oldest snapshot
  value=$((${value} - 1))
  snap="${name}@${label}"
  issnap ${snap}.${value} && /sbin/zfs destroy ${snap}.${value}

  # Increment existing snapshots
  while [ ${value} -gt 0 ]; do
    next=$((${value} - 1))
    issnap ${snap}.${next} && /sbin/zfs rename "${snap}.${next}" "${snap}.${value}"
    value=$next
  done

  # Make new snapshot
  /sbin/zfs snapshot ${snap}.0
done

Gör skriptet exekverbart av root:

root # chmod u+x /root/bin/zfs-autosnap.sh

Crontab

För att automatiskt rotera varje timme, dagligen och varje vecka, kör kommandot crontab och lägg till följande rader:

@hourly /root/bin/zfs-autosnap.sh hourly
@daily	/root/bin/zfs-autosnap.sh daily
@weekly /root/bin/zfs-autosnap.sh weekly

Rotera snapshots

För att rotera snapshots på ett ZFS filsystem, sätter man egenskapen: org.freebsd:snap:{hourly|daily|weekly}=<count>. Antal snapshots innan rotering, styrs via <count> variabeln. Sätts t.ex. värdet till 7, kommer snapshots med nummer 0,1, ..., 6 dvs 7 stycken snapshots sparas. Den senaste snapshot:en är alltid nummer 0.

Exempel: Skapa snapshots av trunk/home/peter dagligen, spara 7 stycken innan den äldsta raderas:

root # zfs set org.freebsd:snap:daily=7 trunk/home/peter