Sparsify a qemu disk with backing file.

sparsify_method1.sh

#!/bin/bash

# Implement method 1 to compress the VM differencing disks.

LIBVIRT_IMAGES=/var/lib/libvirt/images
TARGET_DOMAIN=${1}

function sparsify {
  local TARGET_DISK=${1}
  # Print the size of the differencing disk.
  ls -al ${LIBVIRT_IMAGES}/${TARGET_DISK}*
  # Print out the qemu image information on this target disk.
  qemu-img info ${LIBVIRT_IMAGES}/${TARGET_DISK}

  # Create a new differencing disk over the current differencing disk.
  qemu-img convert -c -f qcow2 -O qcow2 -o backing_file=${LIBVIRT_IMAGES}/${TARGET_DISK}.BASE ${LIBVIRT_IMAGES}/${TARGET_DISK} /tmp/${TARGET_DISK}.sparse1
  # Reclaim the freespace in the new disk.
  virt-sparsify --in-place /tmp/${TARGET_DISK}.sparse1
  # Pull out the non-free blocks from the 2nd disk.
  qemu-img convert -c -f qcow2 -O qcow2 -o backing_file=${LIBVIRT_IMAGES}/${TARGET_DISK}.BASE /tmp/${TARGET_DISK}.sparse1 /tmp/${TARGET_DISK}.sparse2
  echo "Created disk /tmp/${TARGET_DISK}.sparse2."
  # Print out the size of the new differencing disk.
  ls -al /tmp/${TARGET_DISK}*
  qemu-img info /tmp/${TARGET_DISK}.sparse2
  # Remove the first sparse disk.
  rm -v /tmp/${TARGET_DISK}.sparse1
}

virsh shutdown ${TARGET_DOMAIN}
sleep 5

# Find the differencing disks for the domain.
pushd ${LIBVIRT_IMAGES}
DISKS=`ls ${TARGET_DOMAIN}*.qcow2`
popd
# Sparsify each disk individually
for DISK in ${DISKS}; do
  sparsify ${DISK}
done
# Collect all the results in one file.
tar -cvzf ${TARGET_DOMAIN}.tar.gz /tmp/${TARGET_DOMAIN}*
# Remove temporary files.
rm -v /tmp/${TARGET_DOMAIN}*
# Print the name of the tar file.
echo "Created ${TARGET_DOMAIN}.tar.gz with the sparse files for ${TARGET_DOMAIN}"