#crypt device
cryptsetup -y -c aes-cbc-essiv:sha256 -s 256 luksFormat /dev/"device_name"
 
#open device
cryptsetup luksOpen /dev/"device_name" "crypt_name"
 
#make filesystem
mkfs.ext4 /dev/mapper/"crypt_name"
 
#mount and fill with random data (fast way)
mount /dev/mapper/"crypt_name" /mnt/
randfs /mnt/random.file
 
#umount and close crypt
umount /mnt/
cryptsetup luksClose "crypt_name"

randfs

#create file crypt.aes 100MB
dd if=/dev/urandom of=./crypt.aes bs=2k count=50000
#setup loop, you will be prompted for passphrase
losetup -e aes /dev/loop0 ./crypt.aes
#make FS
mkfs.ext3 /dev/loop0
#release loop
losetup -d /dev/loop0

edit /etc/fstab

/crypt.aes /mnt/       ext3    noauto,encryption=aes   0       0