Add support for full allocation (writing zeroes)

  # Create an empty file

  if [ "$ALLOCATE" != "Y" ]; then

  if [ "$ALLOCATE" = "N" ]; then

    truncate -s "${DATA_SIZE}" "${DATA}"

      echo "ERROR: Specify a smaller size or disable preallocation with ALLOCATION=N." && exit 86

    fi

    if [ "$ALLOCATE" = "F" ]; then

      MB=$(( (DATA_SIZE + 1048575)/1048576 ))

      echo "INFO: Writing ${MB} MB of zeroes, please wait.."

      dd if=/dev/zero of="${DATA}" count="${MB}" bs=1M

      truncate -s "${DATA_SIZE}" "${DATA}"

    else

      if ! fallocate -l "${DATA_SIZE}" "${DATA}"; then

        rm -f "${DATA}"

        echo "ERROR: Could not allocate a file for the virtual disk." && exit 87

      fi

    fi

  fi

  # Check if file exists

  if [ ! -f "${DATA}" ]; then

    echo "ERROR: Virtual DSM data disk does not exist ($DATA)" && exit 88

    echo "ERROR: Virtual disk does not exist ($DATA)" && exit 88

  fi

  # Check the filesize

  SIZE=$(stat -c%s "${DATA}")

  if [[ SIZE -ne DATA_SIZE ]]; then

    rm -f "${DATA}"

    echo "ERROR: Virtual disk has the wrong size: ${SIZE}" && exit 89

  fi

  # Format as BTRFS filesystem