There are a two different pages that address how to setup manual full disk encryption "LVM on LUKS". There are a few differences between the askubuntu answer and blog.botux.fr entry
The mount point names are different (cryptcherries vs CryptDisk) but this has no functional impact
The askubuntu answer explains how to zero out the newly created encrypted disk after the sudo cryptsetup luksOpen /dev/sda3 cryptcherries which the blog.botux.fr entry does not.