cheap-snapshot.sh

   1 #!/bin/sh
   2
   3 set -e
   4 set -x
   5
   6 BASE="$1"
   7 BASEDUP="basedup"
   8 ORIGIN="origin"
   9 TOP="top"
  10 COWFILE="/tmp/cowfile"
  11
  12 [ -e "/dev/mapper/$BASE" ] || exit 1
  13
  14 [ -e "$COWFILE" ] || exit 1
  15
  16 COWDEVICE="$(losetup -sf $COWFILE)"
  17
  18 echo 3 > /proc/sys/vm/drop_caches
  19
  20 # Copy the base's table onto basedup
  21 dmsetup table $BASE | dmsetup create $BASEDUP
  22
  23 # Prepare COW image
  24 CHUNK=8
  25 dd if=/dev/zero of=$COWDEVICE bs=512 count=$CHUNK
  26
  27 # Create a snapshot
  28 echo 0 $(blockdev --getsize /dev/mapper/$BASEDUP) \
  29         snapshot /dev/mapper/$BASEDUP $COWDEVICE p 8 | \
  30         dmsetup create $TOP
  31
  32 # Suspend I/O to base
  33 dmsetup suspend $BASE
  34 echo "Snapshot as of"
  35 date
  36
  37 echo 0 $(blockdev --getsize /dev/mapper/$BASEDUP) \
  38         snapshot-origin /dev/mapper/$BASEDUP | \
  39         dmsetup create $ORIGIN
  40
  41 dmsetup table $ORIGIN | dmsetup load $BASE
  42
  43 dmsetup resume $BASE