Essentially all we’ll be doing is generating a key, keeping that on our main drive, and mount our secondary drive using that key.

Format the drive

Let’s find out drive

lsblk

NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
sda           8:0    0   2.7T  0 disk
├─sda1        8:1    0   128M  0 part
└─sda2        8:2    0   2.7T  0 part
sdb           8:16   0 111.8G  0 disk
└─sdb1        8:17   0 111.8G  0 part

Let’s say we want to format the sdb drive.

Format it using sgdisk (pacman -S gptfdisk)

sgdisk -Z /dev/sdb

Create a new partition.

sgdisk -n 1:/dev/sdb1 /dev/sdb

Encrypt the drive

CRYPT_NAME is the name we’ll use for our crypt map. I like to keep it the same as the alias for the drive.

cryptsetup luksFormat --type luks2 /dev/sdb1
cryptsetup luksOpen /dev/sdb1 linuxroot

Create the file system 

mkfs.btrfs -f -L DRIVE_NAME /dev/mapper/DRIVE_NAME

Generating the key

KEY_NAME is whatever you want the name of the key to be. For convenience you could use an alias for the drive, if you want to obscure it it could be random text.

Generate the key:

dd if=/dev/random bs=32 count=1 of=/root/KEY_NAME

Change they key’s permission to readonly for root.

sudo chmod 0400 /root/KEY_NAME

Adding the key

Add our key to the partition (note it is sdb1 not sdb).

cryptsetup luksAddKey /dev/sdb1 /root/KEY_NAME

Add the drive to crypttab

First we want to get the UUID of our partition.

sudo blkid -o value -s UUID /dev/sdb1

Make note of it.

Now add the following line to /etc/crypttab (replacing the values DRIVE_NAME, UUID_VALUE and KEY_NAME).

DRIVE_NAME UUID=UUID_VALUE /root/KEY_NAME

Mount using fstab

First you want to make the mountpoint.

mkdir -p /media/DRIVE_NAME

Final stretch, add this line to /etc/fstab

/dev/mapper/DRIVE_NAME /media/DRIVE_NAME btrfs defaults,nofail 0 0

Moment of truth

Verify there aren’t any errors in fstab.

sudo findmnt --verify --verbose

I like to softlink some of the larger directories under home to my secondary drive.

rm -rf ~/Documents
ln -s /media/DRIVE_NAME/Documents/ ~/Documents