bug#72889: I thought of a possible way to do this.

[amano.kenji]

- /dev/sda

/dev/sda1: A tiny LUKS partition that's filled with the content of a keyfile 
without any filesystem format.
/dev/sda2: /boot for grub. It also serves as FAT32 EFI partition.

- /dev/sdb

/dev/sdb1: /gnu/store on btrfs raid1
/dev/sdb2: / on btrfs raid1 on LUKS

- /dev/sdc

/dev/sdc1: /gnu/store on btrfs raid1
/dev/sdc2: / on btrfs raid1 on LUKS

Open /dev/sda1 as a luke device, /dev/mapper/key, with one password. It 
contains a keyfile without any filesystem format. Use /dev/mapper/key as a 
keyfile for all other LUKS devices in mapped devices.

This exposes /gnu/store, but /gnu/store is not supposed to have any sensitive 
data. This obviously makes it practically impossible to detect physical 
tempering of data, but if you store it at a secure location, you don't have to 
worry too much about evil maid attack.

RAID1 for physically secure servers is enough to ensure some availability when 
a disk fails.

For laptops that you carry, you are not going to use btrfs raid1, and you can 
just have unencrypted /boot on fat32 and / on btrfs on luks. extra-initrd 
contains a keyfile for / so that I don't have to type the password twice.

A desktop computer doesn't require server-level availability, but people who 
have money can still put root on encrypted btrfs raid1.

Perhaps, can this be documented in the cook book?