Firstly, you'd probably want to make backups of the USB device with the initrd, in case one of them fails. To mount the decrypted disk during boot, it's necess

Firstly, you'd probably want to make backups of the USB device with the initrd, in case one of them fails. To mount the decrypted disk during boot, it's necessary to make the kernel aware of the fact that it's something that should be mounted. There are several ways to do this, two of which are: 1. The most preferable way, I think, would be to use something like kpartx from multipath-tools. Kpartx is a very simple C program, and device mapper is used directly in that case. You could also use partprobe. So the command is something like `kpartx -a disk` or `partprobe disk`. 2. Another option is to use LVM, like described here: https://wiki.archlinux.org/title/Dm-crypt/Encrypting_an_entire_system#Plain_dm-crypt https://wiki.archlinux.org/title/Dm-crypt/Encrypting_an_enti... (there are also other encryption options described there). Using LVM is a solution that works more out-of-the-box, but, of course, then you always depends on LVM, which may not be something you want.