Arch Linux : encrypt an external USB drive

Howto encrypt an external USB drive

scenario:

USB drive for backups. 
connected usb drive is sdb with one partition sdb1.

1. create and open luks partition

    cryptsetup -c aes-xts-plain64 -y -s 512 luksFormat /dev/sdb1
    cryptsetup luksOpen /dev/sdb1 backup_drive
   

2. create filesystem on decrypted partition

    mkfs.ext4	/dev/mapper/backup_drive
   

   close the luks container:

    cryptsetup luksClose /dev/mapper/backup_drive
   

3. Using the encrypted drive 3.1 Mount

   cryptsetup luksOpen /dev/sdb1 backup_drive mount /dev/mapper/backup_drive /mnt

3.1 Umount

umount /mnt
cryptsetup luksClose /dev/mapper/backup_drive