Encrypt partition

$ sudo cryptsetup -y -v luksFormat /dev/xvdc 
WARNING!
========
This will overwrite data on /dev/xvdc irrevocably.

Are you sure? (Type uppercase yes): YES
Enter passphrase: 
Verify passphrase: 
Command successful.

Create mapping

cryptsetup luksOpen /dev/xvdc backup2

Format partition

pv -tpreb /dev/zero | dd of=/dev/mapper/backup2 bs=128M
mkfs.ext4 /dev/mapper/backup2

Unmount

umount /backup2
cryptsetup luksClose backup2

Mount

cryptsetup luksOpen /dev/xvdc backup2
mount /dev/mapper/backup2 /backup2