Pavel Kogan has an excellent guide to install Arch Linux with full disk encryption. I've taken the liberty of copying the instructions, adding a couple tweaks:

  1. Boot the Arch Linux installation medium.
  2. Run these commands (You may want to use different sizes for swap and root volumes): 
    parted -s /dev/sda mklabel msdos
parted -s /dev/sda mkpart primary 2048s 100%
parted -s /dev/sda set 1 boot on
cryptsetup luksFormat /dev/sda1
cryptsetup luksOpen /dev/sda1 lvm
pvcreate /dev/mapper/lvm
vgcreate vg /dev/mapper/lvm
lvcreate -L 4G vg -n swap
lvcreate -L 15G vg -n root
lvcreate -l +100%FREE vg -n home
mkswap -L swap /dev/mapper/vg-swap
mkfs.ext4 /dev/mapper/vg-root
mkfs.ext4 /dev/mapper/vg-home
mount /dev/mapper/vg-root /mnt
mkdir /mnt/home
mount /dev/mapper/vg-home /mnt/home
  3. Go through the software installation steps of the installation guide, skipping the Initramfs and Boot loader steps.
  4. Install GRUB: pacman --sync --noconfirm grub
  5. In /etc/mkinitcpio.conf:
    • Change the line starting with FILES= to FILES="/crypto_keyfile.bin"
    • On the line starting with HOOKS= add lvm2 encrypt just before filesystems.
  6. Find the UUID of /dev/sda1 by running basename "$(find -L /dev/disk/by-uuid -samefile /dev/sda1)"
  7. In /etc/default/grub:
    • Change the line starting with GRUB_CMDLINE_LINUX= to GRUB_CMDLINE_LINUX="cryptdevice=UUID=[UUID]:lvm", replacing [UUID] with your own.
    • Add a line with GRUB_ENABLE_CRYPTODISK=y
  8. Run these commands: 
    dd bs=512 count=4 if=/dev/urandom of=/crypto_keyfile.bin
cryptsetup luksAddKey /dev/sda1 /crypto_keyfile.bin
chmod 000 /crypto_keyfile.bin
chmod -R 700 /boot
mkinitcpio -p linux
grub-mkconfig -o /boot/grub/grub.cfg
grub-install --target=i386-pc /dev/sda
  9. If necessary, set up your BIOS to allow booting in CSM mode.

It also required me to enter the password using a QWERTY keymap. The instructions to add an alternative keymap to GRUB are rather involved, but I'll try to write them up if I go through with it.